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P0122 Code Explained: Throttle/Pedal Position Sensor “A” Circuit Low Input Causes, Symptoms & Fixes

P0122 code illustration showing a throttle body and accelerator pedal position sensor with a low-voltage circuit warning, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com

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:

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:

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:

These values are general examples only.

Some sensors operate differently. Depending on the vehicle:

The PCM may store P0122 when the signal falls:

P0122 Quick Facts

ItemInformation
Diagnostic CodeP0122
Generic DefinitionThrottle/Pedal Position Sensor/Switch “A” Circuit Low Input
SystemElectronic throttle, pedal position, and engine management
Fault TypeLow-voltage electrical circuit fault
Common SymptomsReduced power, poor throttle response, rough idle, stalling
Common CausesShort to ground, missing reference voltage, failed sensor, wiring damage
SeverityModerate to high
Safe to Drive?Usually not recommended
Typical Repair Cost$100–$1,200+
Related CodesP0120, 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:

  1. The driver presses the accelerator pedal.
  2. Pedal-position sensors report the requested acceleration.
  3. The PCM calculates the desired throttle opening.
  4. The PCM commands the electronic throttle motor.
  5. Throttle-position sensors confirm actual throttle movement.
  6. 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:

The throttle body may contain:

The PCM compares the signals to detect:

The signals may not display identical values.

For example:

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:

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:

A low signal may result from:

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:

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:

A low Sensor “A” signal may cause the PCM to:

How the PCM Detects P0122

The PCM may set P0122 when it detects:

The code may set:

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:

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:

Pattern 2: Sensor A Remains Low While Sensor B Changes

Possible causes:

Pattern 3: Both Sensor Signals Are Low

Possible causes:

Pattern 4: Signal Drops Low During Acceleration

Possible causes:

Pattern 5: Signal Returns When Another Sensor Is Disconnected

Possible causes:

Pattern 6: Throttle Position Is Low but Actual Throttle Is Open

Possible causes:

Common Symptoms of P0122

P0122 symptoms may include:

Check Engine Light

The Check Engine Light may appear by itself or alongside warnings such as:

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:

The exact response depends on:

No Throttle Response

A severe low-input fault may cause the PCM to ignore the accelerator pedal.

The engine may:

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:

Rough Idle

Incorrect throttle-position data can interfere with:

The engine may:

Stalling

P0122 may cause stalling:

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:

No-Start Condition

P0122 can contribute to a no-start condition, especially if:

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:

Surging and Bucking

A signal that repeatedly falls low and recovers can cause:

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:

Transmission Shift Problems

Throttle and pedal data are important inputs for automatic transmission control.

P0122 may cause:

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 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:

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:

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:

Do not drive if:

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:

Does P0122 Mean the Throttle Position Sensor Is Bad?

Not necessarily.

A failed TPS can cause P0122, but the code can also result from:

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:

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:

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:

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:

Common short locations include:

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:

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:

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:

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:

Can Corrosion Cause P0122?

Yes.

Corrosion can create:

Inspect connectors for:

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:

Can a Vacuum Leak Cause P0122?

A vacuum leak does not normally cause P0122 directly.

It can cause:

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:

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

CodeMeaning
P0120Throttle/Pedal Position Sensor A circuit malfunction
P0121Sensor A range/performance problem
P0122Sensor A circuit low input
P0123Sensor A circuit high input
P0124Sensor A circuit intermittent
P0220Throttle/Pedal Position Sensor B circuit malfunction
P0222Sensor B circuit low input
P2135Throttle 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:

Common P0123 causes include:

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:

  1. Signal wire shorted to ground
  2. Failed throttle-position sensor
  3. Failed accelerator-pedal position sensor
  4. Failed electronic throttle body
  5. Missing five-volt reference
  6. Shared five-volt reference pulled low
  7. Open reference-voltage wire
  8. Broken signal wire
  9. High-resistance signal wire
  10. Poor sensor ground
  11. Shared low-reference fault
  12. Loose throttle-body connector
  13. Loose accelerator-pedal connector
  14. Broken connector lock
  15. Weak terminal tension
  16. Backed-out terminal
  17. Bent connector pin
  18. Corroded connector terminals
  19. Water intrusion
  20. Oil contamination
  21. Heat-damaged wiring
  22. Chafed engine harness
  23. Pinched interior harness
  24. Poor previous wiring repair
  25. Aftermarket pedal controller
  26. Incorrectly installed TPS
  27. Incorrect TPS adjustment
  28. Low battery or charging voltage
  29. PCM connector problem
  30. PCM failure or software issue

1. Signal Wire Shorted to Ground

A short to ground may force the Sensor A voltage to:

This is one of the most common electrical causes of P0122.

2. Failed Throttle-Position Sensor

A TPS may fail because of:

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:

13. Loose Accelerator-Pedal Connector

Pedal connectors may be damaged by:

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:

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:

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

SymptomMost Likely Causes
Sensor A fixed at zeroShort to ground, missing reference, open signal
Both throttle sensors read lowShared reference or ground fault
Pedal Sensor A low but Sensor B normalPedal assembly or Sensor A wiring
Throttle Sensor A low but Sensor B normalThrottle body or Sensor A wiring
Several unrelated sensor codesShared five-volt reference pulled low
Code appears over bumpsLoose terminal or broken conductor
Code appears after intake repairThrottle connector or harness damage
Code appears after interior workPedal connector or wiring damage
Reduced Engine PowerPedal sensor, throttle body, reference fault
Engine only idlesFail-safe mode due to unreliable throttle data
No start with multiple codesShared five-volt circuit short
P0122 and P2135 togetherSensor 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:

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:

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:

Throttle-body cleaning should only be performed when deposits or binding are actually present.

P0122 and Throttle Relearn

A relearn may be required after:

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:

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:

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:

Common symptoms include:

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:

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:

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:

The electronic throttle motor may move when:

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:

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:

Do not clear the code before saving freeze-frame information.

Freeze-frame data may show that the fault occurred:

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:

Common related codes include:

Use the code combination to guide the diagnosis.

Code PatternLikely Diagnostic Direction
P0122 onlySensor A signal, connector, or wiring
P0122 with P0120General Sensor A circuit failure
P0122 with P2135Sensor A low causing A/B disagreement
P0122 with P0222Shared reference or ground issue
P0122 with several pressure-sensor codesShared five-volt reference pulled low
P0122 with pedal-position codesPedal assembly or pedal wiring
P0122 with throttle-actuator codesThrottle body, motor, or connector
P0122 with low-voltage codesBattery, charging, or PCM power problem

Step 3: Identify Sensor “A”

Consult the factory wiring diagram and service information.

Determine whether P0122 refers to:

Record:

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:

During cranking, voltage should remain above the manufacturer’s minimum specification.

With the engine running, charging voltage commonly falls near:

Check for:

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:

Look for:

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:

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:

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:

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:

At rest, the signals should be:

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:

If Sensor A remains low, determine whether:

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:

Repeat the sweep:

Watch for:

Step 12: Compare Sensor A With Sensor B

Redundant sensors should maintain a predictable relationship.

Depending on the system:

Do not compare them by appearance alone.

Use the manufacturer’s expected relationship.

Possible patterns include:

Sensor A Low, Sensor B Normal

Suspect:

Both Sensors Low

Suspect:

Pedal Signals Normal, Throttle Sensor A Low

Suspect:

Pedal Sensor A Low, Throttle Signals Normal

Suspect:

Step 13: Measure Sensor A Signal Voltage

Backprobe the correct Sensor A signal wire.

Many analog position sensors may produce approximately:

These values are only general examples.

A P0122 condition may show:

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:

Zero Volts

Possible causes include:

Reference Voltage Below Specification

Possible causes include:

Battery Voltage on the Five-Volt Circuit

Possible causes include:

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:

When factory procedures permit:

  1. Monitor reference voltage.
  2. Disconnect shared sensors one at a time.
  3. Observe whether voltage returns to normal.
  4. Inspect the branch associated with the change.
  5. 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:

The voltage drop should remain within specification.

Excessive voltage drop may indicate:

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:

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:

Step 19: Check for High Resistance

High resistance may result from:

Compare signal voltage at:

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:

Watch for:

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:

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:

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:

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:

  1. Disconnect the sensor.
  2. Identify the correct terminals.
  3. Measure resistance.
  4. Move the throttle slowly.
  5. Watch for smooth change.

Replace the sensor if resistance:

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:

Perform a slow throttle or pedal sweep.

A normal waveform should appear smooth and consistent.

A faulty waveform may show:

Repeat the test while:

A multimeter may average a brief dropout and hide the failure.

Step 26: Test the Accelerator-Pedal Position Sensor

Graph both pedal signals.

Confirm:

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:

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:

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:

Possible patterns include:

Commanded Angle Changes but Actual Angle Does Not

Suspect:

Actual Angle Changes but Sensor A Remains Low

Suspect:

Both Position Sensors Remain Low

Suspect:

Step 30: Compare Throttle Data With MAP and MAF

Actual throttle opening should generally correspond with changes in:

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:

Remove or bypass aftermarket devices according to their instructions before continuing diagnosis.

Step 32: Review Recent Repairs

P0122 may appear after:

Look for:

Step 33: Check for Technical Service Bulletins

Search manufacturer information for bulletins involving:

A manufacturer bulletin may identify a known wiring location or revised component.

Step 34: Verify PCM Power and Grounds

Before considering PCM failure, verify:

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:

Correct at Sensor but Low at PCM

Suspect:

Low at Both Locations

Suspect:

Step 36: Consider PCM Software

Some vehicles may require an updated calibration for:

Programming should only be performed with:

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:

PCM replacement may require:

How to Fix P0122

The correct repair depends on the test results.

Common P0122 repairs include:

Throttle Position Sensor Replacement

This procedure applies only when the TPS is serviceable separately.

A general replacement process may include:

  1. Turn the ignition off.
  2. Disconnect the battery when required.
  3. Disconnect the TPS connector.
  4. Mark the sensor position if adjustable.
  5. Remove the mounting screws.
  6. Remove the sensor carefully.
  7. Install the new sensor in the correct orientation.
  8. Adjust closed-throttle voltage when required.
  9. Tighten fasteners to specification.
  10. Reconnect the wiring.
  11. Perform relearn or calibration.
  12. Verify live data.

Most modern electronic throttle bodies do not use a separately replaceable TPS.

Electronic Throttle-Body Replacement

A general procedure may include:

  1. Turn the ignition off.
  2. Disconnect the battery when specified.
  3. Remove the intake duct.
  4. Disconnect the electrical connector.
  5. Disconnect coolant hoses if equipped.
  6. Remove the throttle-body bolts.
  7. Remove the throttle body.
  8. Clean the mounting surface.
  9. Install a new gasket.
  10. Install the replacement throttle body.
  11. Torque bolts evenly.
  12. Reconnect hoses and wiring.
  13. Refill and bleed coolant if required.
  14. Perform throttle relearn.
  15. Clear codes.
  16. Verify commanded and actual throttle data.

Do not reuse a damaged throttle-body gasket.

Accelerator-Pedal Assembly Replacement

A general procedure may include:

  1. Turn the ignition off.
  2. Disconnect the battery when required.
  3. Disconnect the pedal connector.
  4. Remove mounting fasteners.
  5. Remove the pedal assembly.
  6. Install the new assembly.
  7. Tighten fasteners correctly.
  8. Reconnect the wiring.
  9. Check for floor-mat interference.
  10. Perform calibration when required.
  11. Verify both pedal signals.

Connector Repair

Replace a connector or pigtail when it has:

Use:

Signal-Wire Repair

Repair a signal wire by:

  1. Locating the damaged section.
  2. Removing all corroded or damaged copper.
  3. Using the correct automotive wire gauge.
  4. Making a sealed crimp or approved splice.
  5. Applying adhesive-lined heat shrink.
  6. Supporting the repair.
  7. Protecting it with loom or harness tape.
  8. 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:

  1. Identify every shared sensor.
  2. Disconnect each branch as permitted.
  3. Monitor reference voltage.
  4. Find the branch that restores voltage.
  5. Inspect that branch for a short.
  6. Test the sensor.
  7. Repair wiring or replace the failed component.
  8. Reconnect all sensors.
  9. Confirm normal reference voltage.
  10. Clear codes and retest.

Ground Repair

Repair poor sensor or PCM grounds by:

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:

  1. Turn the ignition off.
  2. Remove the intake duct.
  3. Inspect the throttle bore.
  4. Apply approved cleaner to a cloth.
  5. Remove deposits carefully.
  6. Avoid flooding the electronics.
  7. Do not scratch protective coatings.
  8. Reinstall the intake duct.
  9. Perform throttle or idle relearn.
  10. Verify operation.

Cleaning will not fix a signal wire shorted to ground.

Throttle Relearn Procedures

A relearn may be required after:

Possible relearn methods include:

Use the manufacturer’s procedure.

Common Relearn Requirements

The vehicle may require:

A relearn may fail when any required condition is not met.

How to Verify the P0122 Repair

After repairs:

  1. Clear codes.
  2. Cycle the ignition as instructed.
  3. Perform the required relearn.
  4. Start the engine.
  5. Verify stable idle.
  6. Check Sensor A voltage.
  7. Check Sensor B voltage.
  8. Sweep the pedal slowly.
  9. Confirm smooth signal movement.
  10. Compare commanded and actual throttle angle.
  11. Perform a road test.
  12. Recheck pending codes.
  13. Confirm reduced-power mode does not return.
  14. Verify cruise and traction systems.
  15. 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:

Monitor:

Stop the test if throttle response becomes unpredictable.

Common P0122 Scan Patterns and Likely Causes

Scan PatternLikely Cause
Sensor A fixed at zeroShort to ground, missing reference, open signal
Sensor A low but Sensor B normalSensor A failure or individual circuit fault
Both throttle signals lowShared reference or ground
Pedal Sensor A low onlyPedal assembly or pedal wiring
Several sensors read lowShared five-volt reference pulled down
Signal drops when harness movesBroken conductor or loose terminal
Signal correct at sensor but low at PCMWiring resistance or connector fault
Code returns when hotHeat-sensitive sensor or wiring
Code returns over bumpsLoose connector or terminal tension
P0122 and P2135 togetherSensor A low causing correlation failure
Engine only idlesElectronic throttle fail-safe mode
Code started after aftermarket controllerPedal-controller fault or installation issue

P0122 Repair Costs

Repair costs vary by vehicle, labor rate, and component design.

RepairTypical 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:

Professional diagnosis may be better when:

Common P0122 Diagnostic Mistakes

Replacing the Throttle Body Immediately

The actual fault may be:

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:

Some GM throttle-position sensors are integrated into the throttle body.

Ford and Lincoln

Use enhanced scan data to compare:

Inspect harness routing near the throttle body and engine.

Toyota and Lexus

Toyota electronic throttle systems use redundant throttle and pedal signals.

Compare:

Initialization may be required after replacement.

Honda and Acura

Inspect:

OEM-quality replacement components are recommended because incorrect signal scaling can cause recurring faults.

Nissan and Infiniti

Nissan vehicles may require:

Follow the exact model-specific procedure.

Hyundai and Kia

Check for:

Use enhanced data to compare both channels.

Volkswagen and Audi

Throttle-body basic settings or adaptation may be required after:

Verify that adaptation completes successfully.

BMW and MINI

BMW may use manufacturer-specific fault descriptions involving:

Use BMW-capable diagnostics rather than relying only on the generic P0122 description.

Mercedes-Benz

Inspect:

Manufacturer-level diagnostic equipment may be needed.

Subaru

Inspect:

Idle relearn may be required after throttle service.

Chrysler, Dodge, Jeep and Ram

An electronic throttle-control warning may accompany P0122.

Check:

Cycling the ignition may temporarily restore operation without correcting the fault.

Preventing Future P0122 Problems

Help prevent future faults by:

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:

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

Throttle/Pedal Position Sensor B Codes

Complete OBD-II Code Libraries

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