If your OBD-II scanner displays P0122, your vehicle’s Engine Control Module or Powertrain Control Module has detected that the Throttle/Pedal Position Sensor “A” circuit voltage is lower than the expected operating range.
The generic OBD-II definition for P0122 is:
Throttle/Pedal Position Sensor/Switch “A” Circuit Low Input
Depending on the vehicle, Sensor “A” may refer to:
- Throttle Position Sensor A
- Throttle Position Sensor 1
- Accelerator Pedal Position Sensor A
- Accelerator Pedal Position Sensor 1
- A primary throttle-angle signal
- A primary accelerator-pedal signal
- An internal sensor inside an electronic throttle body
- A redundant drive-by-wire input monitored by the PCM
P0122 is more specific than the broader P0120 circuit-malfunction code.
While P0120 indicates a general fault in the Sensor “A” circuit, P0122 means the PCM has detected a signal voltage that is consistently too low.
Common causes include:
- A signal wire shorted to ground
- A missing five-volt reference
- A failed throttle-position sensor
- A failed accelerator-pedal position sensor
- A damaged electronic throttle body
- A poor electrical connection
- Corroded terminals
- A broken signal wire
- A high-resistance sensor ground
- A shared five-volt reference circuit pulled low by another sensor
- PCM connector damage
- PCM failure
On an older cable-operated throttle body, the repair may involve a serviceable throttle-position sensor.
On a newer drive-by-wire system, the throttle-position sensors may be permanently integrated into the electronic throttle body. The accelerator-pedal sensors may also be built into the complete pedal assembly.
That means the word “sensor” does not always imply a small, inexpensive part attached with two screws.
Sometimes it means the manufacturer packaged the sensor inside a much larger and considerably more enthusiastic invoice.
What Does the P0122 Code Mean?
P0122 means the PCM has detected that the voltage from Throttle/Pedal Position Sensor “A” is below the calibrated minimum for the current operating condition.
The PCM expects the Sensor “A” signal to remain within a specific voltage range.
On many analog throttle-position sensors, the voltage may begin somewhere around:
- 0.3 to 1.0 volts near the closed-throttle position
- 4.0 to 4.8 volts near wide-open throttle
These values are general examples only.
Some sensors operate differently. Depending on the vehicle:
- The signal may rise as the throttle opens.
- The signal may fall as the throttle opens.
- Sensor A and Sensor B may move in opposite directions.
- The sensor may use a digital output.
- The scan tool may display percentage rather than voltage.
- The circuit may refer to the accelerator pedal rather than the throttle body.
The PCM may store P0122 when the signal falls:
- Below a fixed voltage threshold
- Below the expected voltage for a specified time
- Below the value expected from the redundant sensor
- Below the position commanded by the throttle motor
- Below the position requested by the accelerator pedal
- To nearly zero volts
- Outside the expected mathematical relationship with Sensor B
P0122 Quick Facts
| Item | Information |
|---|---|
| Diagnostic Code | P0122 |
| Generic Definition | Throttle/Pedal Position Sensor/Switch “A” Circuit Low Input |
| System | Electronic throttle, pedal position, and engine management |
| Fault Type | Low-voltage electrical circuit fault |
| Common Symptoms | Reduced power, poor throttle response, rough idle, stalling |
| Common Causes | Short to ground, missing reference voltage, failed sensor, wiring damage |
| Severity | Moderate to high |
| Safe to Drive? | Usually not recommended |
| Typical Repair Cost | $100–$1,200+ |
| Related Codes | P0120, P0121, P0123, P0124, P0222, P2135 |
What Is Throttle/Pedal Position Sensor “A”?
Throttle and accelerator-pedal position sensors tell the PCM how much throttle opening or driver demand is present.
On a cable-operated throttle system, the throttle pedal mechanically opens the throttle plate through a cable.
The Throttle Position Sensor measures the throttle shaft angle and sends that information to the PCM.
On a drive-by-wire system:
- The driver presses the accelerator pedal.
- Pedal-position sensors report the requested acceleration.
- The PCM calculates the desired throttle opening.
- The PCM commands the electronic throttle motor.
- Throttle-position sensors confirm actual throttle movement.
- The PCM compares all signals continuously.
Sensor “A” generally identifies the primary signal in a redundant system.
The exact component must be confirmed using vehicle-specific service information.
Why Electronic Throttle Systems Use Multiple Sensors
Electronic throttle systems normally use redundant sensors for safety.
The accelerator pedal may contain:
- Pedal Position Sensor A
- Pedal Position Sensor B
The throttle body may contain:
- Throttle Position Sensor A
- Throttle Position Sensor B
The PCM compares the signals to detect:
- Low-voltage faults
- High-voltage faults
- Signal dropouts
- Mechanical sticking
- Sensor disagreement
- Unintended throttle movement
- Wiring problems
The signals may not display identical values.
For example:
- Sensor A may rise from low to high voltage.
- Sensor B may fall from high to low voltage.
- One sensor may operate at half the voltage of the other.
- The PCM may expect a specific combined value.
- The sensors may use different percentage scales.
A difference between the two readings is not automatically a failure.
The problem occurs when their relationship falls outside the manufacturer’s programmed limits.
How a Throttle Position Sensor Works
A throttle-position sensor may use:
- A potentiometer
- A Hall-effect sensor
- A magnetoresistive sensor
- An integrated electronic circuit
Potentiometer-Type Throttle Position Sensor
A potentiometer uses a resistive track and movable contact.
As the throttle shaft rotates, the sensor’s output voltage changes.
The sensor generally receives:
- Five-volt reference
- Sensor ground
- Signal return
A low signal may result from:
- A worn resistive track
- An internal short
- A shorted signal wire
- Missing reference voltage
- Excessive ground resistance
- Incorrect sensor alignment
Hall-Effect Throttle Position Sensor
A Hall-effect sensor measures changes in a magnetic field.
It has no traditional sliding electrical contact, but it can still fail because of:
- Internal electronic damage
- Supply-voltage problems
- Ground faults
- Connector damage
- Temperature-related failure
- Magnetic or mechanical alignment issues
How the Accelerator Pedal Position Sensor Works
The accelerator-pedal assembly may contain two or more sensors.
As the pedal moves, each sensor sends a signal to the PCM.
The PCM uses these signals to determine:
- Driver torque request
- Desired throttle angle
- Transmission torque management
- Cruise-control behavior
- Traction-control intervention
- Stability-control operation
A low Sensor “A” signal may cause the PCM to:
- Ignore the pedal input
- Limit throttle opening
- Enter limp mode
- Hold the engine near idle
- Disable cruise control
- Store correlation codes
- Illuminate an electronic throttle warning
How the PCM Detects P0122
The PCM may set P0122 when it detects:
- Sensor A voltage below the calibrated minimum
- Voltage near zero
- A signal shorted to ground
- No five-volt reference
- A signal that remains too low as the throttle opens
- A signal inconsistent with Sensor B
- A pedal request that does not match throttle movement
- A low signal lasting longer than a calibrated time
- A low signal during startup
- A low signal under specific operating conditions
The code may set:
- Immediately when the ignition is turned on
- During cranking
- At idle
- During acceleration
- When the harness moves
- After the engine warms up
- Only when another sensor pulls down the shared reference circuit
What Does “Circuit Low Input” Mean?
“Circuit low input” means the PCM sees a voltage lower than expected on the Sensor “A” signal circuit.
This does not always mean the sensor itself is defective.
A low signal can be caused by:
- Signal wire shorted to ground
- Reference voltage missing
- Sensor ground problem
- Failed sensor
- Corroded connector
- Damaged harness
- Another sensor pulling down a shared circuit
- PCM input failure
P0122 describes the electrical condition.
It does not identify the failed part.
Common P0122 Scan-Tool Patterns
Pattern 1: Sensor A Stuck at Zero Percent
Possible causes:
- Signal shorted to ground
- Open reference circuit
- Failed sensor
- Disconnected connector
- Broken signal wire
- PCM input problem
Pattern 2: Sensor A Remains Low While Sensor B Changes
Possible causes:
- Sensor A failure
- Sensor A signal-wire fault
- Connector-terminal problem
- Internal throttle-body or pedal failure
Pattern 3: Both Sensor Signals Are Low
Possible causes:
- Missing five-volt reference
- Shared sensor-ground fault
- Shared connector problem
- PCM power or ground issue
- Another sensor pulling down the reference circuit
Pattern 4: Signal Drops Low During Acceleration
Possible causes:
- Harness movement
- Broken conductor
- Loose terminal
- Engine movement pulling the connector
- Worn sensor area
Pattern 5: Signal Returns When Another Sensor Is Disconnected
Possible causes:
- Shared five-volt reference circuit short
- Failed MAP sensor
- Failed pressure sensor
- Shorted harness branch
- Failed pedal or throttle sensor
Pattern 6: Throttle Position Is Low but Actual Throttle Is Open
Possible causes:
- Incorrect position feedback
- Internal throttle-body sensor fault
- Signal circuit short
- PCM input issue
Common Symptoms of P0122
P0122 symptoms may include:
- Check Engine Light
- Reduced Engine Power warning
- Electronic Throttle Control warning
- Limp mode
- No throttle response
- Delayed throttle response
- Limited acceleration
- Engine speed limited
- Rough idle
- Low idle
- High idle
- Stalling
- Hard starting
- No-start condition
- Hesitation
- Surging
- Bucking
- Poor fuel economy
- Black smoke
- Misfires
- Transmission shift problems
- Cruise control disabled
- Traction-control warning
- Stability-control warning
- Engine may only idle
- Throttle response may return after restarting
Check Engine Light
The Check Engine Light may appear by itself or alongside warnings such as:
- Reduced Engine Power
- Electronic Throttle Control
- Traction Control Disabled
- Stability Control Disabled
- Cruise Control Unavailable
- Service Engine Soon
- Wrench warning light
Multiple warning lights do not necessarily indicate several unrelated failures.
Throttle-position data is used by many systems, so one low-voltage sensor fault can trigger warnings throughout the vehicle.
Reduced Engine Power Mode
The PCM may limit engine output when it cannot trust the throttle or pedal signal.
Reduced-power strategies may include:
- Limiting throttle opening
- Limiting RPM
- Ignoring part of the pedal travel
- Holding the throttle near idle
- Disabling cruise control
- Restricting transmission torque
- Limiting vehicle speed
- Using the remaining redundant sensor
The exact response depends on:
- Which sensor failed
- Whether the fault is intermittent
- Whether Sensor B remains plausible
- Whether the throttle body still responds
- Manufacturer programming
No Throttle Response
A severe low-input fault may cause the PCM to ignore the accelerator pedal.
The engine may:
- Start normally
- Idle normally
- Refuse to accelerate
- Respond only slightly
- Remain locked in fail-safe mode
A vehicle with unreliable throttle response should not be driven in traffic.
Poor or Delayed Acceleration
The vehicle may respond slowly when the pedal is pressed.
Possible behavior includes:
- Delayed engine response
- Limited throttle opening
- Hesitation
- Sudden reduced-power mode
- Inability to merge safely
- Poor hill-climbing performance
- Engine speed capped at a low RPM
Rough Idle
Incorrect throttle-position data can interfere with:
- Idle control
- Fuel delivery
- Ignition timing
- Load calculation
- Electronic throttle angle
- Transmission engagement
The engine may:
- Surge
- Shake
- Hunt
- Idle too low
- Idle too high
- Stall when accessories turn on
- Stall when the transmission is placed in gear
Stalling
P0122 may cause stalling:
- At idle
- When coming to a stop
- During deceleration
- When shifting into gear
- When the throttle closes
- During startup
- During parking maneuvers
Stalling occurs when the PCM cannot correctly manage throttle position, fuel delivery, or idle airflow.
Hard Starting
A low throttle-position or pedal-position signal may disrupt startup calculations.
The engine may:
- Crank longer than normal
- Start and immediately stall
- Require several attempts
- Run poorly after starting
- Enter limp mode immediately
No-Start Condition
P0122 can contribute to a no-start condition, especially if:
- The five-volt reference circuit is pulled down
- Several engine sensors stop operating
- The throttle body fails initialization
- The PCM cannot verify pedal or throttle position
- The electronic throttle remains in an invalid position
If several unrelated sensor codes appear with P0122, inspect the shared five-volt reference circuit.
Hesitation
The engine may hesitate because the PCM sees less throttle opening or pedal request than actually exists.
The PCM may reduce:
- Fuel delivery
- Ignition timing
- Throttle command
- Transmission torque
Surging and Bucking
A signal that repeatedly falls low and recovers can cause:
- Surging
- Bucking
- Jerking
- Uneven acceleration
- Intermittent limp mode
- Sudden loss of power
Although P0122 usually indicates a consistently low signal, loose connections may cause the signal to alternate between normal and low.
High Idle
A low Sensor “A” signal can occasionally result in a fixed fail-safe throttle position.
The vehicle may idle higher than normal because the PCM chooses a predetermined throttle angle to keep the engine running.
High idle can also result from:
- Throttle-body contamination
- Incorrect relearn
- Vacuum leaks
- Mechanical sticking
- Mismatched Sensor A and Sensor B signals
Transmission Shift Problems
Throttle and pedal data are important inputs for automatic transmission control.
P0122 may cause:
- Harsh shifts
- Delayed shifts
- Early shifts
- Late shifts
- Limited gear operation
- Torque-converter lockup disabled
- Reduced transmission torque
- Transmission limp mode
Repair P0122 before assuming that harsh shifting means the transmission itself has failed.
Cruise Control Disabled
Cruise control requires reliable pedal and throttle-position information.
The system may be disabled until P0122 is repaired.
Traction and Stability Control Warnings
Traction and stability systems control engine torque through the electronic throttle.
If the throttle system cannot be trusted, these features may be disabled.
Poor Fuel Economy
Incorrect throttle-position information can affect:
- Fuel injection
- Ignition timing
- Engine load calculation
- Transmission shifting
- Idle speed
- Torque management
Fuel economy may drop, particularly if the engine operates in a backup strategy.
Black Smoke
Black smoke is possible if the fault causes an incorrect rich condition.
Additional symptoms may include:
- Fuel odor
- Sooty exhaust
- Fouled spark plugs
- Poor fuel economy
- Catalytic-converter overheating
Black smoke is not the most common P0122 symptom, but it should not be ignored.
Is P0122 Serious?
P0122 should be considered a moderate-to-high severity code.
The fault can affect:
- Throttle response
- Engine power
- Acceleration
- Idle quality
- Starting
- Transmission operation
- Cruise control
- Traction control
- Stability control
- Emissions
- Vehicle safety
The vehicle may enter reduced-power mode without warning.
A throttle-control fault becomes a safety issue when the driver cannot accurately control acceleration.
Can You Drive With P0122?
Driving with P0122 is generally not recommended.
A very short trip may be possible if:
- Throttle response is normal
- The vehicle is not in limp mode
- The engine is not stalling
- Acceleration remains predictable
- No electronic throttle warning is active
Do not drive if:
- The accelerator pedal does not respond
- The vehicle enters Reduced Engine Power mode
- The engine stalls
- Engine speed changes unexpectedly
- Acceleration is severely limited
- Multiple throttle-control codes are present
- The throttle works only after restarting the engine
Have the vehicle towed if throttle response is unpredictable.
Can P0122 Cause Limp Mode?
Yes.
Limp mode is one of the most common responses to P0122 on drive-by-wire vehicles.
The PCM may:
- Restrict engine speed
- Limit throttle opening
- Ignore part of the pedal signal
- Disable cruise control
- Disable traction control
- Hold the throttle in a fixed position
Does P0122 Mean the Throttle Position Sensor Is Bad?
Not necessarily.
A failed TPS can cause P0122, but the code can also result from:
- Shorted signal wiring
- Missing five-volt reference
- Loose connectors
- Corroded terminals
- Poor sensor ground
- Failed accelerator-pedal sensor
- Shared reference circuit faults
- Electronic throttle-body failure
- PCM connector damage
The complete circuit should be tested before replacing parts.
Can a Bad Accelerator Pedal Sensor Cause P0122?
Yes.
On some vehicles, Sensor “A” refers to the primary accelerator-pedal position circuit.
A failed pedal sensor may cause:
- No throttle response
- Reduced-power mode
- Pedal correlation faults
- Low pedal-position data
- Intermittent acceleration
- Cruise-control failure
Many accelerator-pedal sensors are serviced only as a complete pedal assembly.
Can a Bad Electronic Throttle Body Cause P0122?
Yes.
Electronic throttle bodies commonly contain:
- Throttle Position Sensor A
- Throttle Position Sensor B
- Throttle motor
- Internal wiring
- Position electronics
- Reduction gears
If Sensor A fails internally, the complete throttle body may require replacement.
Can a Dirty Throttle Body Cause P0122?
A dirty throttle body usually does not directly cause a low electrical input.
Carbon buildup may contribute to:
- Mechanical sticking
- Incorrect closed-throttle position
- Motor overload
- Correlation faults
- Idle problems
P0122 primarily indicates a low-voltage circuit problem.
Cleaning the throttle body should not replace electrical diagnosis.
Can a Short to Ground Cause P0122?
Yes.
A signal wire shorted to ground is one of the most direct causes of P0122.
The PCM may see:
- Zero volts
- Near-zero volts
- A value below the expected minimum
- Sensor position fixed at zero percent
Common short locations include:
- Harness rubbing against engine brackets
- Wiring melted near exhaust components
- Pinched wires
- Damaged connector terminals
- Failed previous repairs
- Water-contaminated connectors
Can a Missing Five-Volt Reference Cause P0122?
Yes.
Most analog throttle and pedal-position sensors require a regulated reference voltage from the PCM.
If the five-volt supply is missing, Sensor A may output little or no voltage.
Possible causes include:
- Open reference wire
- Short to ground
- Failed shared sensor
- Corroded splice
- PCM regulator fault
- Damaged connector
Can Another Sensor Cause P0122?
Yes.
Several sensors may share the same five-volt reference circuit.
A failed sensor elsewhere may pull the entire reference voltage low.
Possible shared sensors include:
- MAP sensor
- Fuel-pressure sensor
- A/C pressure sensor
- Fuel-tank pressure sensor
- Transmission pressure sensor
- Accelerator-pedal sensor
- Throttle-position sensor
If several unrelated sensor codes appear together, inspect the shared reference circuit before replacing the throttle body.
Can a Poor Ground Cause P0122?
Yes.
A high-resistance sensor ground can interfere with the circuit’s voltage relationship.
Depending on the sensor design, a ground fault may cause:
- Low signal voltage
- Erratic signal
- Correlation codes
- Sensor readings stuck at one value
- Multiple sensor faults
Continuity alone may not reveal the problem.
A loaded voltage-drop test is more useful.
Can a Broken Signal Wire Cause P0122?
Yes.
An open signal wire may cause the PCM input to default low.
The conductor may be broken inside insulation that appears undamaged.
The fault may become worse when:
- The engine moves
- The harness warms up
- The vehicle travels over bumps
- The connector is disturbed
- The pedal is pressed
Can Corrosion Cause P0122?
Yes.
Corrosion can create:
- High resistance
- Signal loss
- Reference-voltage loss
- Ground problems
- Intermittent contact
- Terminal damage
Inspect connectors for:
- Green deposits
- White residue
- Moisture
- Darkened copper
- Loose terminal fit
Can Low Battery Voltage Cause P0122?
Low system voltage may contribute to throttle-control faults, but it is not usually the primary direct cause of P0122.
Check the battery and charging system when the code appears with:
- Low-voltage codes
- Communication faults
- Multiple module warnings
- Throttle initialization faults
- Recent jump-start history
- Slow cranking
Can a Vacuum Leak Cause P0122?
A vacuum leak does not normally cause P0122 directly.
It can cause:
- High idle
- Lean codes
- Hesitation
- Surging
- Poor fuel economy
These symptoms may resemble a throttle problem, but P0122 specifically indicates a low electrical input.
Can a Bad PCM Cause P0122?
PCM failure is possible but uncommon.
Possible PCM-related causes include:
- Failed five-volt regulator
- Damaged sensor input
- Water intrusion
- Connector-terminal failure
- Internal ground fault
- Software issue
The PCM should be suspected only after the sensor, wiring, connectors, reference voltage, grounds, and shared circuits have been tested.
P0122 Compared With Related Codes
| Code | Meaning |
| P0120 | Throttle/Pedal Position Sensor A circuit malfunction |
| P0121 | Sensor A range/performance problem |
| P0122 | Sensor A circuit low input |
| P0123 | Sensor A circuit high input |
| P0124 | Sensor A circuit intermittent |
| P0220 | Throttle/Pedal Position Sensor B circuit malfunction |
| P0222 | Sensor B circuit low input |
| P2135 | Throttle Position Sensor A/B voltage correlation |
P0122 vs. P0120
P0120 is a general Sensor A circuit-malfunction code.
P0122 specifically means the Sensor A voltage is too low.
P0122 vs. P0121
P0121 means the signal exists but does not match the expected range or performance.
P0122 means the voltage is below the calibrated minimum.
P0122 vs. P0123
P0122 indicates a low-input condition.
P0123 indicates a high-input condition.
Common P0122 causes include:
- Short to ground
- Missing reference voltage
- Failed low-output sensor
Common P0123 causes include:
- Signal shorted to voltage
- Open ground
- Failed high-output sensor
P0122 vs. P0124
P0124 means the Sensor A signal is intermittent.
P0122 means the signal remains lower than expected long enough to meet the code-setting criteria.
P0122 vs. P0222
P0122 usually refers to Sensor A.
P0222 usually refers to Sensor B or another throttle/pedal circuit, depending on manufacturer definitions.
P0122 vs. P2135
P2135 indicates that Throttle Position Sensor A and Sensor B do not agree.
P0122 specifically indicates that Sensor A is too low.
Both codes may appear together if Sensor A fails.
30 Common Causes of P0122
The most common causes include:
- Signal wire shorted to ground
- Failed throttle-position sensor
- Failed accelerator-pedal position sensor
- Failed electronic throttle body
- Missing five-volt reference
- Shared five-volt reference pulled low
- Open reference-voltage wire
- Broken signal wire
- High-resistance signal wire
- Poor sensor ground
- Shared low-reference fault
- Loose throttle-body connector
- Loose accelerator-pedal connector
- Broken connector lock
- Weak terminal tension
- Backed-out terminal
- Bent connector pin
- Corroded connector terminals
- Water intrusion
- Oil contamination
- Heat-damaged wiring
- Chafed engine harness
- Pinched interior harness
- Poor previous wiring repair
- Aftermarket pedal controller
- Incorrectly installed TPS
- Incorrect TPS adjustment
- Low battery or charging voltage
- PCM connector problem
- PCM failure or software issue
1. Signal Wire Shorted to Ground
A short to ground may force the Sensor A voltage to:
- Zero volts
- Near zero
- Below the PCM threshold
This is one of the most common electrical causes of P0122.
2. Failed Throttle-Position Sensor
A TPS may fail because of:
- Worn resistive track
- Internal short
- Hall-effect circuit failure
- Heat damage
- Moisture
- Mechanical wear
3. Failed Accelerator-Pedal Position Sensor
A pedal sensor may fail internally and produce a consistently low signal.
The complete pedal assembly may require replacement.
4. Failed Electronic Throttle Body
If the throttle-position sensor is integrated, internal failure may require replacement of the complete throttle body.
5. Missing Five-Volt Reference
Without the correct reference supply, the sensor cannot generate a normal output.
6. Shared Five-Volt Reference Pulled Low
Another failed sensor may short the shared reference circuit.
This can generate multiple sensor codes simultaneously.
7. Open Reference-Voltage Wire
A broken reference wire may remove sensor power even though the sensor and signal wire remain intact.
8. Broken Signal Wire
An open signal wire may cause the PCM to read a low default voltage.
9. High-Resistance Signal Wire
Corrosion or a damaged splice may reduce the voltage reaching the PCM.
10. Poor Sensor Ground
Ground resistance can distort the signal and cause low or implausible readings.
11. Shared Low-Reference Fault
Several sensors may share a ground splice or PCM low-reference terminal.
12. Loose Throttle-Body Connector
A connector that is not fully seated may interrupt:
- Reference voltage
- Signal
- Ground
- Throttle motor circuits
13. Loose Accelerator-Pedal Connector
Pedal connectors may be damaged by:
- Foot traffic
- Carpet
- Water
- Interior work
- Aftermarket wiring
14. Broken Connector Lock
A broken lock allows vibration to loosen the connection.
15. Weak Terminal Tension
A terminal may appear clean but fail to grip the sensor pin firmly.
16. Backed-Out Terminal
A terminal may push backward when the connector is installed.
17. Bent Connector Pin
A bent pin may not make proper electrical contact.
18. Corroded Connector Terminals
Corrosion increases resistance and may interrupt sensor power or signal.
19. Water Intrusion
Water can enter through damaged seals, flooding, engine cleaning, or interior leaks.
20. Oil Contamination
Oil can soften connector seals and trap conductive debris.
21. Heat-Damaged Wiring
Wiring near the engine may be damaged by:
- Exhaust heat
- Turbochargers
- Cylinder heads
- Intake manifolds
- EGR components
22. Chafed Engine Harness
Harness contact with metal brackets can wear through insulation and short the signal to ground.
23. Pinched Interior Harness
Pedal wiring may be trapped beneath:
- Carpet
- Trim panels
- Dash brackets
- Screws
- Aftermarket modules
24. Poor Previous Wiring Repair
Unsealed splices, incorrect terminals, and damaged copper may create excessive resistance.
25. Aftermarket Pedal Controller
A pedal booster or throttle controller intercepts accelerator-pedal signals.
A failed or improperly installed unit may cause P0122.
26. Incorrectly Installed TPS
On older systems, the sensor may be installed in the wrong rotational position.
27. Incorrect TPS Adjustment
Some older adjustable sensors require a specific closed-throttle voltage.
28. Low Battery or Charging Voltage
Low system voltage can interfere with throttle initialization and module operation.
29. PCM Connector Problem
Loose, corroded, or water-damaged PCM terminals may prevent the correct signal from reaching the module.
30. PCM Failure or Software Issue
PCM failure is rare but possible after all external circuits have been tested.
Most Likely Causes by Symptom
| Symptom | Most Likely Causes |
| Sensor A fixed at zero | Short to ground, missing reference, open signal |
| Both throttle sensors read low | Shared reference or ground fault |
| Pedal Sensor A low but Sensor B normal | Pedal assembly or Sensor A wiring |
| Throttle Sensor A low but Sensor B normal | Throttle body or Sensor A wiring |
| Several unrelated sensor codes | Shared five-volt reference pulled low |
| Code appears over bumps | Loose terminal or broken conductor |
| Code appears after intake repair | Throttle connector or harness damage |
| Code appears after interior work | Pedal connector or wiring damage |
| Reduced Engine Power | Pedal sensor, throttle body, reference fault |
| Engine only idles | Fail-safe mode due to unreliable throttle data |
| No start with multiple codes | Shared five-volt circuit short |
| P0122 and P2135 together | Sensor A low causing correlation failure |
Common Vehicles Affected by P0122
P0122 is a generic OBD-II code that may appear on most 1996-and-newer vehicles, including models from:
- Chevrolet
- GMC
- Buick
- Cadillac
- Ford
- Lincoln
- Mercury
- Toyota
- Lexus
- Honda
- Acura
- Nissan
- Infiniti
- Hyundai
- Kia
- Subaru
- Volkswagen
- Audi
- BMW
- MINI
- Mercedes-Benz
- Chrysler
- Dodge
- Jeep
- Ram
- Mazda
- Mitsubishi
- Volvo
The exact Sensor “A” circuit and testing procedure vary by model.
P0122 and Reduced Engine Power
P0122 commonly triggers a reduced-power strategy because the PCM cannot trust the primary throttle or pedal signal.
The vehicle may use Sensor B as a backup, but engine output may remain limited.
Do not assume that restarting the engine has repaired the problem if normal throttle response temporarily returns.
P0122 and Shared Five-Volt Reference Circuits
A shared five-volt circuit deserves special attention when P0122 appears with several unrelated sensor codes.
For example, a shorted pressure sensor may pull reference voltage low for:
- Throttle position
- Pedal position
- MAP
- A/C pressure
- Fuel pressure
The scanner may then suggest that half the engine compartment failed simultaneously.
It probably did not.
One shared electrical fault can create an impressive pile of codes.
P0122 and Throttle-Body Cleaning
Cleaning may improve mechanical throttle operation, but it will not repair:
- A shorted signal wire
- Missing five-volt reference
- Broken connector
- Failed sensor electronics
- Corroded terminals
- Poor ground
Throttle-body cleaning should only be performed when deposits or binding are actually present.
P0122 and Throttle Relearn
A relearn may be required after:
- Throttle-body replacement
- Throttle-body cleaning
- TPS replacement
- Accelerator-pedal replacement
- Battery disconnection
- PCM replacement
- Software programming
A missing relearn typically causes idle or performance problems, but electrical testing should still be completed when P0122 is stored.
P0122 and Emissions Testing
A vehicle with P0122 will usually fail an emissions inspection because:
- The Check Engine Light is illuminated
- The code is stored
- Readiness monitors may be incomplete
- Throttle and fuel control may be affected
Clearing the code without repairing the fault resets the monitors and delays the inevitable reunion with the warning light.
Can P0122 Clear Itself?
The Check Engine Light may turn off after several fault-free drive cycles.
However:
- The code may remain stored in history.
- A permanent code may remain.
- Reduced-power mode may return.
- The low-voltage fault may still be present.
- The problem may become more frequent.
Throttle-position faults should be diagnosed even if the warning temporarily disappears.
Final Thoughts
The P0122 Throttle/Pedal Position Sensor “A” Circuit Low Input code means the PCM has detected that the primary throttle or accelerator-pedal position signal is below its expected electrical range.
The most common causes include:
- Signal wire shorted to ground
- Missing five-volt reference
- Failed throttle-position sensor
- Failed pedal-position sensor
- Electronic throttle-body failure
- Damaged wiring
- Loose connectors
- Corroded terminals
- Poor sensor ground
- Shared reference-voltage faults
Common symptoms include:
- Reduced Engine Power
- Limp mode
- Limited acceleration
- No throttle response
- Rough idle
- Stalling
- Hard starting
- Transmission shift problems
- Cruise-control failure
- Traction-control warnings
P0122 does not automatically mean the throttle body must be replaced.
The correct diagnosis begins by identifying which Sensor “A” circuit the vehicle uses and then testing:
- Live throttle data
- Accelerator-pedal data
- Five-volt reference
- Sensor ground
- Signal voltage
- Connector integrity
- Wiring continuity
- Shared reference circuits
The continuation of this guide covers complete P0122 diagnosis, live-data graphing, voltage testing, shared five-volt circuit isolation, throttle and pedal sensor testing, wiring repair, component replacement, relearn procedures, repair costs, manufacturer-specific tips, and common diagnostic mistakes.
How to Diagnose the P0122 Code
Diagnosing P0122 requires proving why the Throttle/Pedal Position Sensor “A” signal is lower than expected.
The code does not automatically identify a failed throttle-position sensor.
Depending on the vehicle, the problem may involve:
- A serviceable throttle-position sensor
- An internal sensor inside the electronic throttle body
- An accelerator-pedal position sensor
- A complete pedal assembly
- A signal wire shorted to ground
- A missing five-volt reference
- A damaged sensor-ground circuit
- A shared reference-voltage fault
- Loose or corroded connector terminals
- A PCM input problem
The most important first step is determining exactly what the manufacturer calls Sensor “A” on that particular vehicle.
On one model, P0122 may refer to the primary throttle-position sensor.
On another, it may refer to the accelerator-pedal position sensor.
On some systems, the generic code description may not match the terminology used in the factory service manual.
Parts stores may appreciate guessing. Diagnostic accuracy generally does not.
P0122 Safety Precautions
Electronic throttle-control systems are safety-critical.
Before beginning diagnosis:
- Park the vehicle on a level surface.
- Apply the parking brake.
- Place the transmission in Park or Neutral.
- Keep hands away from the electronic throttle plate.
- Do not place fingers inside the throttle body with the ignition on.
- Follow manufacturer instructions before disconnecting the PCM.
- Disconnect the battery before wiring repairs unless live testing is required.
- Use fused jumper wires when directed.
- Never apply battery voltage to a five-volt sensor circuit.
- Do not force an electronic throttle plate unless the manufacturer permits it.
- Keep the battery supported during extended ignition-on testing.
The electronic throttle motor may move when:
- The ignition is switched on
- The PCM performs a self-test
- A scan-tool actuator test is commanded
- The accelerator pedal is pressed
- The vehicle exits reduced-power mode
Treat the throttle plate as a powered component, not a convenient place to rest a screwdriver or fingertip.
Tools Needed to Diagnose P0122
A complete P0122 diagnosis may require:
- OBD-II scan tool
- Scan tool with live-data graphing
- Manufacturer-capable diagnostic software
- Digital multimeter
- Oscilloscope
- Backprobe leads
- Fused jumper wires
- Terminal-tension test kit
- Wiring diagrams
- Factory service information
- Battery charger or maintainer
- Electrical contact cleaner
- Throttle-body cleaner
- Basic hand tools
- Infrared thermometer
- Smoke machine when intake leaks are also suspected
A basic code reader can identify P0122, but it may not display the throttle and pedal data needed to locate the fault.
Step 1: Confirm the Code
Connect the scan tool and record:
- Stored codes
- Pending codes
- Permanent codes
- Freeze-frame data
- Battery voltage
- Engine speed
- Vehicle speed
- Throttle Position Sensor A
- Throttle Position Sensor B
- Accelerator Pedal Position Sensor A
- Accelerator Pedal Position Sensor B
- Commanded throttle angle
- Actual throttle angle
- Engine load
- MAP data
- MAF data
Do not clear the code before saving freeze-frame information.
Freeze-frame data may show that the fault occurred:
- During startup
- At idle
- During acceleration
- During deceleration
- At a specific engine temperature
- At low battery voltage
- At a certain throttle angle
- When the vehicle was stationary
This information can help reproduce the failure.
Step 2: Check for Related Trouble Codes
P0122 rarely exists in complete isolation on a severe electronic throttle fault.
Look for related codes involving:
- Sensor A
- Sensor B
- Accelerator-pedal position
- Throttle actuator control
- Throttle correlation
- Five-volt reference
- System voltage
- PCM communication
- MAP sensor
- Fuel-pressure sensor
- A/C pressure sensor
Common related codes include:
- P0120
- P0121
- P0123
- P0124
- P0220
- P0221
- P0222
- P0223
- P0224
- P0638
- P2100
- P2101
- P2107
- P2111
- P2112
- P2120
- P2122
- P2127
- P2135
- P2138
Use the code combination to guide the diagnosis.
| Code Pattern | Likely Diagnostic Direction |
|---|---|
| P0122 only | Sensor A signal, connector, or wiring |
| P0122 with P0120 | General Sensor A circuit failure |
| P0122 with P2135 | Sensor A low causing A/B disagreement |
| P0122 with P0222 | Shared reference or ground issue |
| P0122 with several pressure-sensor codes | Shared five-volt reference pulled low |
| P0122 with pedal-position codes | Pedal assembly or pedal wiring |
| P0122 with throttle-actuator codes | Throttle body, motor, or connector |
| P0122 with low-voltage codes | Battery, charging, or PCM power problem |
Step 3: Identify Sensor “A”
Consult the factory wiring diagram and service information.
Determine whether P0122 refers to:
- Throttle Position Sensor 1
- Throttle Position Sensor A
- Accelerator Pedal Position Sensor 1
- Accelerator Pedal Position Sensor A
- A primary throttle-feedback circuit
- A primary pedal-request circuit
Record:
- Component location
- Connector pin numbers
- Five-volt reference wire
- Sensor-ground wire
- Signal wire
- Expected closed-position voltage
- Expected open-position voltage
- Sensor A and Sensor B relationship
- Whether the sensor is replaceable separately
- Whether relearn or calibration is required
Do not assume the part is located on the throttle body just because the code contains the word “throttle.”
Step 4: Inspect Battery and Charging Voltage
Electronic throttle systems require stable electrical power.
With the engine off, a fully charged battery commonly measures near:
- 12.6 volts when fully charged
- 12.4 volts when partially charged
- Below 12.2 volts when significantly discharged
During cranking, voltage should remain above the manufacturer’s minimum specification.
With the engine running, charging voltage commonly falls near:
- 13.5 to 14.8 volts
Check for:
- Loose battery terminals
- Corrosion
- Weak grounds
- Damaged engine ground straps
- Alternator ripple
- Recent jump-start history
- Low-voltage codes
Use a battery maintainer during long key-on tests.
Low voltage can distort electronic throttle data or prevent proper initialization.
Step 5: Perform a Full Visual Inspection
Inspect:
- Throttle-body connector
- Accelerator-pedal connector
- PCM connectors
- Harness routing
- Ground connections
- Intake ducting
- Aftermarket wiring
- Previous repair areas
Look for:
- Broken connector locks
- Backed-out terminals
- Bent pins
- Spread terminals
- Green corrosion
- White residue
- Water intrusion
- Oil contamination
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Poor splices
- Rodent damage
- Harness tension
A P0122 fault is often caused by something physically visible before the multimeter ever leaves its case.
Step 6: Inspect the Throttle-Body Connector
Turn the ignition off and disconnect the throttle-body connector.
Inspect for:
- Corrosion
- Moisture
- Oil
- Coolant
- Bent terminals
- Loose terminal fit
- Heat discoloration
- Damaged seals
- Broken locks
- Signs of arcing
Check that the connector locks securely when reinstalled.
A connector may appear seated while one terminal remains pushed backward inside the housing.
Step 7: Inspect the Accelerator-Pedal Connector
Check the pedal connector and harness for:
- Water intrusion
- Carpet interference
- Damage from shoes
- Pinched wires
- Loose mounting
- Previous dashboard repairs
- Alarm wiring
- Remote-start wiring
- Pedal-controller installations
The pedal harness is often ignored because it is inside the cabin.
Unfortunately, it is also located where feet, moisture, trim panels, and questionable aftermarket wiring frequently gather.
Step 8: Check the Throttle Plate
With the ignition off, inspect the throttle bore and plate for:
- Carbon buildup
- Oil deposits
- Foreign material
- Mechanical binding
- Damaged gears
- Ice
- Shaft wear
- Incorrect intake installation
Do not force the plate open unless the manufacturer allows manual movement.
Heavy deposits may cause throttle-control or correlation faults, but P0122 remains an electrical low-input code.
Cleaning should not replace circuit testing.
Step 9: Review Scan-Tool Data at Rest
Turn the ignition on with the engine off.
Observe:
- Sensor A percentage
- Sensor B percentage
- Sensor A voltage
- Sensor B voltage
- Accelerator-pedal position
- Commanded throttle angle
- Actual throttle angle
At rest, the signals should be:
- Stable
- Plausible
- Within specification
- Consistent with each other
A healthy sensor does not necessarily display zero percent at closed throttle.
Some scan tools normalize the data, while others display raw voltage or calculated angle.
Step 10: Check Whether Sensor A Is Fixed Low
A P0122 fault may show:
- Zero percent
- Near-zero voltage
- A value that never changes
- A value lower than Sensor B expects
- A value that drops when the harness moves
If Sensor A remains low, determine whether:
- The sensor has power
- The sensor has ground
- The signal wire reaches the PCM
- The sensor itself can create an output
Step 11: Slowly Sweep the Pedal or Throttle
With the ignition on and engine off, slowly press the accelerator pedal through its full travel.
Graph:
- Pedal Sensor A
- Pedal Sensor B
- Throttle Sensor A
- Throttle Sensor B
- Commanded throttle angle
- Actual throttle angle
Repeat the sweep:
- Slowly
- At moderate speed
- Rapidly
- Through frequently used pedal positions
Watch for:
- Signal stuck low
- Delayed movement
- Sudden dropouts
- Flat spots
- Sensor disagreement
- Failure near one specific position
Step 12: Compare Sensor A With Sensor B
Redundant sensors should maintain a predictable relationship.
Depending on the system:
- Both signals may rise
- One may rise while the other falls
- One may use half the voltage range
- Their combined voltage may remain nearly constant
Do not compare them by appearance alone.
Use the manufacturer’s expected relationship.
Possible patterns include:
Sensor A Low, Sensor B Normal
Suspect:
- Sensor A internal failure
- Sensor A signal-wire short
- Sensor A connector problem
- Individual reference or ground fault
Both Sensors Low
Suspect:
- Shared five-volt reference fault
- Shared ground fault
- Connector issue
- PCM power problem
- Another sensor pulling down the circuit
Pedal Signals Normal, Throttle Sensor A Low
Suspect:
- Electronic throttle body
- Throttle-body connector
- Throttle Sensor A wiring
Pedal Sensor A Low, Throttle Signals Normal
Suspect:
- Accelerator-pedal assembly
- Pedal connector
- Pedal Sensor A circuit
Step 13: Measure Sensor A Signal Voltage
Backprobe the correct Sensor A signal wire.
Many analog position sensors may produce approximately:
- 0.3 to 1.0 volts near the closed position
- 4.0 to 4.8 volts near the fully open position
These values are only general examples.
A P0122 condition may show:
- Zero volts
- Near-zero voltage
- Voltage below specification
- Voltage that does not increase
- Voltage that drops under vibration
Compare the reading with factory specifications.
Step 14: Test the Five-Volt Reference
With the ignition on, measure reference voltage at the sensor connector.
A normal circuit commonly measures near five volts.
Possible results include:
Approximately Five Volts Present
The reference circuit is likely functional.
Continue testing:
- Sensor output
- Ground
- Signal wiring
- Component
Zero Volts
Possible causes include:
- Open reference wire
- Short to ground
- Failed shared sensor
- PCM regulator problem
- Connector fault
Reference Voltage Below Specification
Possible causes include:
- Partial short to ground
- Corroded splice
- Failed sensor loading the circuit
- Harness damage
- PCM fault
Battery Voltage on the Five-Volt Circuit
Possible causes include:
- Short to ignition voltage
- Short to battery voltage
- Incorrect wiring repair
This condition can damage multiple sensors and the PCM.
Step 15: Isolate a Shared Five-Volt Reference Fault
Use the wiring diagram to identify every sensor sharing the reference circuit.
Possible shared sensors include:
- MAP sensor
- Fuel-pressure sensor
- A/C pressure sensor
- Fuel-tank pressure sensor
- Transmission pressure sensor
- Accelerator-pedal sensor
- Throttle-position sensor
When factory procedures permit:
- Monitor reference voltage.
- Disconnect shared sensors one at a time.
- Observe whether voltage returns to normal.
- Inspect the branch associated with the change.
- Test the sensor and wiring separately.
If the five-volt reference returns after disconnecting one component, that sensor or harness branch may be shorted.
Do not automatically replace the disconnected sensor until its wiring has also been checked.
Step 16: Test Sensor Ground
Measure the sensor-ground or low-reference circuit.
Check voltage drop between:
- Sensor ground and battery negative
- Sensor ground and engine ground
- Sensor ground and PCM ground
The voltage drop should remain within specification.
Excessive voltage drop may indicate:
- Corroded splice
- Loose terminal
- Broken wire
- Poor PCM ground
- Connector resistance
A continuity beep does not prove that the ground can carry current correctly.
Step 17: Test the Signal Wire for a Short to Ground
Disconnect the sensor and PCM as required.
Measure resistance between the signal wire and ground.
The circuit should not show unintended continuity.
Inspect likely damage points near:
- Engine brackets
- Intake manifold
- Cylinder head
- Firewall
- Pedal bracket
- Steering column
- Exhaust components
A direct short to ground is one of the most common electrical causes of P0122.
Step 18: Test the Signal Wire for an Open Circuit
Measure resistance from the Sensor A signal terminal to the PCM terminal.
The wire should have very low resistance.
Move the harness during testing.
An internally broken conductor may:
- Pass a stationary continuity test
- Fail when bent
- Fail when hot
- Fail during engine movement
Step 19: Check for High Resistance
High resistance may result from:
- Corrosion
- Loose terminals
- Damaged splices
- Partially broken wires
- Water intrusion
- Poor previous repairs
Compare signal voltage at:
- The sensor
- Midway through the circuit when accessible
- The PCM terminal
A voltage that is correct at the sensor but low at the PCM indicates a wiring or connector problem.
Step 20: Perform a Wiggle Test
Monitor Sensor A voltage or live data while moving:
- Throttle-body connector
- Pedal connector
- Engine harness
- Firewall harness
- PCM connector area
- Shared reference wiring
- Ground splices
Watch for:
- Voltage dropping to zero
- Percentage falling
- Warning lights
- Reduced-power activation
- Code reset
- Signal recovery
If the reading changes when one harness section moves, inspect that area closely.
Step 21: Test Connector Terminal Tension
Use the correct terminal test probes.
Do not insert oversized meter probes into the connector.
Compare suspect terminals with known-good terminals of the same type.
Replace terminals that:
- Fit loosely
- Have lost spring tension
- Are pushed backward
- Show corrosion
- Are heat damaged
Weak terminal tension can cause a circuit-low fault even when the connector appears clean.
Step 22: Load-Test the Reference and Ground Circuits
A wire may show normal voltage with no load and fail when current is drawn.
Use an approved load test for:
- Five-volt reference
- Sensor ground
- Signal circuit
Do not use a high-current incandescent test light on a PCM sensor circuit unless the manufacturer specifically permits it.
Electronic sensor circuits prefer careful testing to enthusiastic improvisation.
Step 23: Sweep-Test the Throttle Position Sensor
This applies mainly to analog potentiometer-type sensors.
Monitor voltage while slowly moving the throttle.
A healthy signal should change smoothly.
A faulty signal may show:
- Flat spots
- Sudden drops
- Zero-voltage areas
- Delayed response
- Irregular steps
- Dead sections
A sensor may fail only at the throttle angle used during normal cruising.
Step 24: Test Sensor Resistance
Only perform resistance testing when the service procedure allows it.
For a serviceable potentiometer-style TPS:
- Disconnect the sensor.
- Identify the correct terminals.
- Measure resistance.
- Move the throttle slowly.
- Watch for smooth change.
Replace the sensor if resistance:
- Drops open
- Jumps suddenly
- Becomes unstable
- Shows dead spots
Do not resistance-test powered Hall-effect sensors unless instructed.
Step 25: Use an Oscilloscope
An oscilloscope is useful for intermittent low-voltage faults.
Connect to:
- Sensor A signal
- Sensor ground
Perform a slow throttle or pedal sweep.
A normal waveform should appear smooth and consistent.
A faulty waveform may show:
- Sudden drop to zero
- Signal clipping
- Missing sections
- Electrical noise
- Brief low-voltage spikes
- Irregular steps
Repeat the test while:
- Moving the harness
- Heating the sensor
- Cooling the sensor
- Applying gentle connector pressure
A multimeter may average a brief dropout and hide the failure.
Step 26: Test the Accelerator-Pedal Position Sensor
Graph both pedal signals.
Confirm:
- Sensor A responds immediately
- Sensor B responds correctly
- Both signals maintain the expected relationship
- Neither signal drops low
- Pedal movement is smooth
- The pedal returns fully
If Pedal Sensor A remains low while Sensor B behaves normally, the pedal assembly or Sensor A circuit may be faulty.
Many pedal-position sensors are not sold separately.
Step 27: Inspect Mechanical Pedal Operation
Check for:
- Floor-mat interference
- Carpet interference
- Bent pedal arm
- Loose mounting
- Broken return spring
- Debris
- Water damage
- Binding
Make sure the pedal moves smoothly and returns to its resting position.
A mechanically damaged pedal can create implausible electrical data even when the sensor has not completely failed.
Step 28: Test the Electronic Throttle Body
If P0122 refers to an internal throttle-position sensor, test:
- Sensor A
- Sensor B
- Reference voltage
- Ground
- Throttle motor
- Commanded angle
- Actual angle
- Internal correlation
If Sensor A is integrated and testing confirms internal failure, the complete throttle body may require replacement.
Step 29: Perform a Bidirectional Throttle Test
A capable scan tool may command the electronic throttle plate.
Compare:
- Commanded angle
- Actual angle
- Sensor A
- Sensor B
- Throttle motor current
Possible patterns include:
Commanded Angle Changes but Actual Angle Does Not
Suspect:
- Throttle motor
- Motor wiring
- Mechanical binding
- Internal gears
Actual Angle Changes but Sensor A Remains Low
Suspect:
- Internal Sensor A failure
- Sensor A signal circuit
- Connector fault
Both Position Sensors Remain Low
Suspect:
- Shared reference
- Shared ground
- Connector power supply
- PCM issue
Step 30: Compare Throttle Data With MAP and MAF
Actual throttle opening should generally correspond with changes in:
- MAP
- MAF
- Engine load
- Engine RPM
If the throttle plate visibly opens and airflow increases while Sensor A remains near zero, the feedback circuit is incorrect.
If pedal position changes but commanded throttle remains fixed, the PCM may be in fail-safe mode.
Step 31: Inspect Aftermarket Pedal Controllers
Aftermarket pedal boosters, throttle controllers, tuners, and piggyback devices may intercept pedal signals.
Inspect for:
- Inline pedal modules
- Poor connector fit
- Bent terminals
- Modified signal wires
- Damaged adapter harnesses
- Improper grounds
Remove or bypass aftermarket devices according to their instructions before continuing diagnosis.
Step 32: Review Recent Repairs
P0122 may appear after:
- Throttle-body replacement
- Throttle cleaning
- Intake-manifold repair
- Engine replacement
- Accelerator-pedal replacement
- Dashboard work
- Remote-start installation
- Battery replacement
- PCM programming
Look for:
- Loose connectors
- Pinched wiring
- Damaged terminals
- Incorrect component installation
- Missing relearn
- Low battery voltage during service
Step 33: Check for Technical Service Bulletins
Search manufacturer information for bulletins involving:
- Throttle-body replacement
- Pedal-sensor failure
- Connector pigtails
- Harness chafing
- Water intrusion
- Shared five-volt circuits
- PCM programming
- Reduced Engine Power
- Throttle relearn
A manufacturer bulletin may identify a known wiring location or revised component.
Step 34: Verify PCM Power and Grounds
Before considering PCM failure, verify:
- Battery feeds
- Ignition feeds
- Ground circuits
- Connector seating
- Terminal tension
- Water intrusion
- Voltage drop under load
PCM power or ground faults may affect several sensor circuits at once.
Step 35: Measure Sensor A at the PCM
If Sensor A voltage is correct at the component but scan data remains low, test the circuit at the PCM terminal.
Possible findings include:
Correct Voltage at Sensor and PCM
Suspect:
- PCM input processing
- Software
- Intermittent fault
- Incorrect PID interpretation
Correct at Sensor but Low at PCM
Suspect:
- Signal-wire resistance
- Partial short to ground
- Connector fault
- Damaged splice
Low at Both Locations
Suspect:
- Sensor
- Reference voltage
- Ground
- Component connector
Step 36: Consider PCM Software
Some vehicles may require an updated calibration for:
- Throttle-control logic
- Pedal plausibility
- Fail-safe strategy
- Idle adaptation
- False code detection
Programming should only be performed with:
- Stable battery voltage
- Approved equipment
- Correct calibration
- Reliable connection
A software update will not repair a physically shorted signal wire.
Step 37: Consider PCM Failure
PCM failure is uncommon.
Suspect the PCM only after confirming:
- Correct sensor
- Correct five-volt reference
- Correct ground
- Intact signal circuit
- Proper terminal tension
- No shared-circuit fault
- Correct component operation
- Updated software
PCM replacement may require:
- Programming
- VIN configuration
- Immobilizer registration
- Key programming
- Throttle relearn
- Security access
How to Fix P0122
The correct repair depends on the test results.
Common P0122 repairs include:
- Reconnecting a loose connector
- Repairing damaged terminals
- Replacing a connector pigtail
- Repairing a shorted signal wire
- Repairing an open reference circuit
- Repairing sensor ground
- Repairing a shared five-volt circuit
- Replacing a serviceable TPS
- Replacing the accelerator-pedal assembly
- Replacing an electronic throttle body
- Removing a faulty pedal controller
- Cleaning the throttle body when binding is present
- Updating PCM software
- Replacing the PCM in rare cases
Throttle Position Sensor Replacement
This procedure applies only when the TPS is serviceable separately.
A general replacement process may include:
- Turn the ignition off.
- Disconnect the battery when required.
- Disconnect the TPS connector.
- Mark the sensor position if adjustable.
- Remove the mounting screws.
- Remove the sensor carefully.
- Install the new sensor in the correct orientation.
- Adjust closed-throttle voltage when required.
- Tighten fasteners to specification.
- Reconnect the wiring.
- Perform relearn or calibration.
- Verify live data.
Most modern electronic throttle bodies do not use a separately replaceable TPS.
Electronic Throttle-Body Replacement
A general procedure may include:
- Turn the ignition off.
- Disconnect the battery when specified.
- Remove the intake duct.
- Disconnect the electrical connector.
- Disconnect coolant hoses if equipped.
- Remove the throttle-body bolts.
- Remove the throttle body.
- Clean the mounting surface.
- Install a new gasket.
- Install the replacement throttle body.
- Torque bolts evenly.
- Reconnect hoses and wiring.
- Refill and bleed coolant if required.
- Perform throttle relearn.
- Clear codes.
- Verify commanded and actual throttle data.
Do not reuse a damaged throttle-body gasket.
Accelerator-Pedal Assembly Replacement
A general procedure may include:
- Turn the ignition off.
- Disconnect the battery when required.
- Disconnect the pedal connector.
- Remove mounting fasteners.
- Remove the pedal assembly.
- Install the new assembly.
- Tighten fasteners correctly.
- Reconnect the wiring.
- Check for floor-mat interference.
- Perform calibration when required.
- Verify both pedal signals.
Connector Repair
Replace a connector or pigtail when it has:
- Broken locking tabs
- Corroded terminals
- Loose terminal fit
- Water damage
- Heat damage
- Missing seals
- Oil contamination
Use:
- Correct terminals
- Correct wire gauge
- Sealed automotive splices
- Adhesive-lined heat shrink
- Proper strain relief
- Factory-style harness routing
Signal-Wire Repair
Repair a signal wire by:
- Locating the damaged section.
- Removing all corroded or damaged copper.
- Using the correct automotive wire gauge.
- Making a sealed crimp or approved splice.
- Applying adhesive-lined heat shrink.
- Supporting the repair.
- Protecting it with loom or harness tape.
- Rerouting it away from heat and sharp edges.
Do not splice into green or blackened copper.
Five-Volt Reference Repair
When another sensor pulls down the reference circuit:
- Identify every shared sensor.
- Disconnect each branch as permitted.
- Monitor reference voltage.
- Find the branch that restores voltage.
- Inspect that branch for a short.
- Test the sensor.
- Repair wiring or replace the failed component.
- Reconnect all sensors.
- Confirm normal reference voltage.
- Clear codes and retest.
Ground Repair
Repair poor sensor or PCM grounds by:
- Cleaning corrosion
- Tightening fasteners
- Replacing damaged terminals
- Repairing broken wiring
- Replacing engine ground straps
- Sealing exposed connections
Verify the repair with a loaded voltage-drop test.
Throttle-Body Cleaning
Cleaning may be appropriate when carbon buildup or sticking is confirmed.
A general procedure may include:
- Turn the ignition off.
- Remove the intake duct.
- Inspect the throttle bore.
- Apply approved cleaner to a cloth.
- Remove deposits carefully.
- Avoid flooding the electronics.
- Do not scratch protective coatings.
- Reinstall the intake duct.
- Perform throttle or idle relearn.
- Verify operation.
Cleaning will not fix a signal wire shorted to ground.
Throttle Relearn Procedures
A relearn may be required after:
- Throttle-body replacement
- Throttle-body cleaning
- TPS replacement
- Pedal assembly replacement
- Battery disconnection
- PCM replacement
- PCM programming
Possible relearn methods include:
- Scan-tool initialization
- Ignition-on waiting period
- Accelerator-pedal sequence
- Idle learning
- Drive cycle
- Throttle closed-position learning
Use the manufacturer’s procedure.
Common Relearn Requirements
The vehicle may require:
- Fully charged battery
- Engine at operating temperature
- Transmission in Park or Neutral
- Steering wheel centered
- Air conditioning off
- Electrical loads off
- No active DTCs
- Pedal fully released
- Stable idle
- Cooling fans off
A relearn may fail when any required condition is not met.
How to Verify the P0122 Repair
After repairs:
- Clear codes.
- Cycle the ignition as instructed.
- Perform the required relearn.
- Start the engine.
- Verify stable idle.
- Check Sensor A voltage.
- Check Sensor B voltage.
- Sweep the pedal slowly.
- Confirm smooth signal movement.
- Compare commanded and actual throttle angle.
- Perform a road test.
- Recheck pending codes.
- Confirm reduced-power mode does not return.
- Verify cruise and traction systems.
- Confirm transmission shifting is normal.
The vehicle should be tested under the same conditions shown in freeze-frame data.
Recommended Road Test
When safe and legal, include:
- Idle operation
- Light acceleration
- Moderate acceleration
- Steady cruising
- Deceleration
- Stop-and-go driving
- Uphill load
- Repeated pedal movement
Monitor:
- Sensor A
- Sensor B
- Accelerator Pedal Position A
- Accelerator Pedal Position B
- Commanded throttle angle
- Actual throttle angle
- MAP
- MAF
- Engine load
- Battery voltage
Stop the test if throttle response becomes unpredictable.
Common P0122 Scan Patterns and Likely Causes
| Scan Pattern | Likely Cause |
| Sensor A fixed at zero | Short to ground, missing reference, open signal |
| Sensor A low but Sensor B normal | Sensor A failure or individual circuit fault |
| Both throttle signals low | Shared reference or ground |
| Pedal Sensor A low only | Pedal assembly or pedal wiring |
| Several sensors read low | Shared five-volt reference pulled down |
| Signal drops when harness moves | Broken conductor or loose terminal |
| Signal correct at sensor but low at PCM | Wiring resistance or connector fault |
| Code returns when hot | Heat-sensitive sensor or wiring |
| Code returns over bumps | Loose connector or terminal tension |
| P0122 and P2135 together | Sensor A low causing correlation failure |
| Engine only idles | Electronic throttle fail-safe mode |
| Code started after aftermarket controller | Pedal-controller fault or installation issue |
P0122 Repair Costs
Repair costs vary by vehicle, labor rate, and component design.
| Repair | Typical Cost |
| Diagnostic testing | $100–$250 |
| Connector cleaning or adjustment | $100–$250 |
| Connector pigtail replacement | $150–$450 |
| Minor wiring repair | $150–$500 |
| Extensive harness repair | $400–$1,500+ |
| Serviceable TPS replacement | $100–$350 |
| Accelerator-pedal assembly | $150–$600 |
| Electronic throttle-body replacement | $300–$1,200+ |
| Throttle-body cleaning | $100–$250 |
| Ground repair | $100–$350 |
| PCM software update | $100–$300 |
| PCM replacement and programming | $1,000–$3,000+ |
Luxury vehicles and applications with integrated throttle-body cooling or complex intake systems may cost more.
Can You Repair P0122 Yourself?
A careful DIY owner may be able to:
- Inspect connectors
- Remove an aftermarket pedal controller
- Check reference voltage
- Check Sensor A voltage
- Inspect wiring
- Clean the throttle body
- Replace a serviceable TPS
- Replace a bolt-on pedal assembly
- Perform some relearn procedures
Professional diagnosis may be better when:
- The vehicle has no throttle response
- Reduced Engine Power is active
- Several sensor codes are present
- Oscilloscope testing is required
- Shared reference circuits are involved
- PCM programming is needed
- The fault is intermittent
- Wiring diagrams are difficult to interpret
Common P0122 Diagnostic Mistakes
Replacing the Throttle Body Immediately
The actual fault may be:
- Signal wire shorted to ground
- Missing reference voltage
- Pedal sensor
- Connector terminal
- Shared reference circuit
Assuming Sensor “A” Is Always on the Throttle Body
Sensor A may refer to the accelerator pedal.
Always check factory information.
Ignoring the Five-Volt Reference
A failed shared sensor can make the throttle system appear defective.
Replacing Several Sensors at Once
Multiple low-voltage codes often indicate one shared electrical fault.
Cleaning the Throttle Body Instead of Testing the Circuit
Carbon deposits do not repair missing voltage.
Checking Continuity Without a Load
A damaged wire can pass a continuity test but fail in operation.
Ignoring Connector Terminal Tension
Clean-looking terminals may still be loose.
Using Oversized Meter Probes
Large probes can spread terminals and create a new intermittent fault.
Forgetting Aftermarket Pedal Controllers
Pedal boosters directly modify accelerator signals and can trigger P0122.
Forcing the Electronic Throttle Plate
This may damage internal gears or sensors.
Skipping Relearn Procedures
A replacement or cleaned throttle body may not operate correctly without calibration.
Condemning the PCM Too Soon
PCM failure is far less common than sensor, connector, and wiring problems.
Manufacturer-Specific P0122 Notes
General Motors
GM vehicles may display Reduced Engine Power.
Check:
- Throttle-body connector
- Pedal-position circuits
- Five-volt reference circuits
- Ground splices
- Sensor A and Sensor B correlation
Some GM throttle-position sensors are integrated into the throttle body.
Ford and Lincoln
Use enhanced scan data to compare:
- Desired throttle angle
- Actual throttle angle
- Throttle Position Sensor 1
- Throttle Position Sensor 2
- Accelerator Pedal Position channels
Inspect harness routing near the throttle body and engine.
Toyota and Lexus
Toyota electronic throttle systems use redundant throttle and pedal signals.
Compare:
- Throttle Position Sensor 1 and 2
- Accelerator Pedal Position Sensor 1 and 2
- Commanded throttle angle
Initialization may be required after replacement.
Honda and Acura
Inspect:
- Throttle-body connector
- Accelerator-pedal connector
- Sensor grounds
- Electronic throttle-control wiring
OEM-quality replacement components are recommended because incorrect signal scaling can cause recurring faults.
Nissan and Infiniti
Nissan vehicles may require:
- Accelerator Pedal Released Position Learning
- Throttle Valve Closed Position Learning
- Idle Air Volume Learning
Follow the exact model-specific procedure.
Hyundai and Kia
Check for:
- Connector seal damage
- Harness chafing
- Shared reference faults
- Pedal-signal disagreement
- Throttle-body contamination
Use enhanced data to compare both channels.
Volkswagen and Audi
Throttle-body basic settings or adaptation may be required after:
- Cleaning
- Replacement
- Battery disconnection
- Module programming
Verify that adaptation completes successfully.
BMW and MINI
BMW may use manufacturer-specific fault descriptions involving:
- Pedal-value sensors
- Throttle-valve position
- Plausibility
- Adaptation
Use BMW-capable diagnostics rather than relying only on the generic P0122 description.
Mercedes-Benz
Inspect:
- Pedal-position data
- Throttle-actuator data
- Power and grounds
- Low-voltage history
- Communication faults
Manufacturer-level diagnostic equipment may be needed.
Subaru
Inspect:
- Engine-harness routing
- Pedal and throttle correlation
- Connector fit
- Ground circuits
Idle relearn may be required after throttle service.
Chrysler, Dodge, Jeep and Ram
An electronic throttle-control warning may accompany P0122.
Check:
- Throttle body
- Pedal assembly
- Five-volt reference
- Battery voltage
- Harness connectors
Cycling the ignition may temporarily restore operation without correcting the fault.
Preventing Future P0122 Problems
Help prevent future faults by:
- Keeping connectors dry
- Repairing oil and coolant leaks
- Securing loose harnesses
- Replacing broken connector locks
- Maintaining battery terminals
- Maintaining engine grounds
- Removing poorly installed pedal controllers
- Avoiding aggressive throttle-body cleaning
- Using quality replacement components
- Performing relearn procedures correctly
- Inspecting wiring after engine or dashboard repairs
- Keeping floor mats clear of the accelerator pedal
Frequently Asked Questions About P0122 Diagnosis and Repair
How do you diagnose P0122?
Identify which Sensor A circuit the vehicle uses, inspect connectors, graph live data, verify five-volt reference voltage, check sensor ground, measure the signal, and test the wiring for a short to ground or open circuit.
What usually fixes P0122?
Common fixes include repairing a shorted signal wire, restoring five-volt reference voltage, repairing connectors, replacing a failed TPS, replacing the accelerator-pedal assembly, or replacing an electronic throttle body.
What voltage causes P0122?
The exact threshold varies, but many systems set P0122 when Sensor A falls below approximately 0.2 to 0.5 volts for a calibrated period. Always use vehicle-specific specifications.
Can a short to ground cause P0122?
Yes. A signal wire shorted to ground is one of the most common direct causes.
Can a missing five-volt reference cause P0122?
Yes. Without reference voltage, the sensor may produce little or no output.
Can another sensor cause P0122?
Yes. A failed sensor sharing the same five-volt circuit may pull the entire reference supply low.
Can a bad MAP sensor cause P0122?
It can if the MAP sensor shares and shorts the same five-volt reference circuit.
Does P0122 mean the TPS is bad?
No. The sensor, wiring, connector, reference voltage, ground, pedal assembly, throttle body, or PCM input may be responsible.
How do I know whether the pedal or throttle body is faulty?
Graph pedal data, commanded throttle angle, and actual throttle angle together. Incorrect pedal data points toward the pedal circuit. Correct pedal data with incorrect throttle feedback points toward the throttle body or its wiring.
Can a dirty throttle body cause P0122?
It usually does not directly cause a low electrical input, although severe deposits may create throttle-control or correlation problems.
Can low battery voltage cause P0122?
Low voltage can contribute to electronic throttle faults, especially when other low-voltage or communication codes are present.
Can P0122 cause no throttle response?
Yes. The PCM may ignore the pedal and hold the engine near idle.
Can P0122 cause a no-start?
Yes, especially if a shared five-volt reference fault disables multiple engine sensors.
Can P0122 cause stalling?
Yes. Incorrect throttle data may interfere with idle control and fuel delivery.
Can P0122 affect transmission shifting?
Yes. Throttle and pedal signals influence load calculation, shift timing, and torque management.
Does a new throttle body require relearn?
Many vehicles require throttle adaptation, closed-position learning, or idle relearn after replacement.
Can I replace only the throttle-position sensor?
Only when it is sold separately and the manufacturer provides a replacement procedure. Many modern sensors are integrated into the throttle body.
Can an aftermarket pedal controller cause P0122?
Yes. A failed controller or loose adapter harness may lower or interrupt the pedal signal.
Is an oscilloscope required?
Not always, but it is valuable for finding brief signal dropouts or electrical noise.
Why does P0122 return over bumps?
A loose terminal, broken conductor, or poorly secured connector may lose contact during vibration.
Why does P0122 return when the engine is hot?
Heat may expand a damaged terminal, increase resistance, or trigger an internal sensor failure.
Why do several unrelated sensor codes appear with P0122?
They may share the same five-volt reference or sensor-ground circuit.
Can disconnecting the battery fix P0122?
No. It may temporarily clear codes or reset fail-safe mode, but it will not repair the electrical fault.
How much does P0122 cost to repair?
Costs may range from approximately $100 for a simple connector repair to over $1,200 for throttle-body or harness replacement. PCM replacement can cost considerably more.
Is P0122 safe to drive with?
Generally no. Reduced power, stalling, or unreliable throttle response can make the vehicle unsafe in traffic.
What should I test first?
Check related codes, identify Sensor A, inspect connectors, verify the five-volt reference, check Sensor A voltage, and inspect the signal wire for a short to ground.
Final Thoughts
The P0122 Throttle/Pedal Position Sensor “A” Circuit Low Input code should be diagnosed as an electrical low-voltage fault, not simply as a failed throttle body.
The correct approach is to determine exactly what Sensor A refers to and then test the circuit in a logical order.
Verify:
- Battery voltage
- Related trouble codes
- Sensor A live data
- Sensor B live data
- Five-volt reference
- Sensor ground
- Signal voltage
- Wiring integrity
- Connector terminal tension
- Shared reference circuits
- Commanded and actual throttle movement
If Sensor A is low but Sensor B operates normally, focus on the individual Sensor A circuit or internal sensor.
If both signals are low, focus on shared power, ground, and reference circuits.
If several unrelated sensors also read low, suspect a shared five-volt circuit before replacing multiple components.
P0122 may ultimately require a new throttle-position sensor, pedal assembly, or electronic throttle body. But those parts should be replaced only after the circuit proves they are responsible.
A scanner can tell you that the PCM sees low voltage.
It cannot tell you whether that voltage disappeared inside the sensor, under the dashboard, behind the intake manifold, or inside a connector that looks perfectly innocent.
That part still requires diagnosis.
Related Pro Street Diagnostic Guides
Throttle/Pedal Position Sensor A Codes
- P0120 Code Explained: Throttle/Pedal Position Sensor A Circuit Malfunction
- P0121 Code Explained: Throttle/Pedal Position Sensor A Range/Performance
- P0123 Code Explained: Throttle/Pedal Position Sensor A Circuit High Input
- P0124 Code Explained: Throttle/Pedal Position Sensor A Circuit Intermittent
Throttle/Pedal Position Sensor B Codes
- P0220 Code Explained: Throttle/Pedal Position Sensor B Circuit Malfunction
- P0221 Code Explained: Throttle/Pedal Position Sensor B Range/Performance
- P0222 Code Explained: Throttle/Pedal Position Sensor B Circuit Low Input
- P0223 Code Explained: Throttle/Pedal Position Sensor B Circuit High Input
- P0224 Code Explained: Throttle/Pedal Position Sensor B Circuit Intermittent
