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P0120 Code Explained: Throttle/Pedal Position Sensor “A” Circuit Malfunction Causes, Symptoms & Fixes

P0120 code illustration showing a throttle body, accelerator pedal position sensor, Check Engine Light, wiring diagram, Pro Street TV logo, and www.ProStreetOnline.com.

If your OBD-II scanner displays P0120, your vehicle’s Engine Control Module or Powertrain Control Module has detected a malfunction in the Throttle Position Sensor “A” circuit, Accelerator Pedal Position Sensor “A” circuit, or a related electronic throttle-control input.

The generic OBD-II definition for P0120 is:

Throttle/Pedal Position Sensor/Switch “A” Circuit Malfunction

Depending on the vehicle, P0120 may refer to:

On older cable-operated throttle systems, the code usually points toward a sensor mounted on the throttle body.

On newer drive-by-wire systems, diagnosis may involve:

That distinction matters.

Replacing the throttle-position sensor on a vehicle where the sensor is permanently built into the throttle body is not a repair plan. It is merely a creative way to discover that the sensor is not sold separately.

Common causes include:

What Does the P0120 Code Mean?

P0120 means the PCM has detected a general electrical or performance problem involving the throttle or accelerator-pedal position Sensor “A” circuit.

The PCM expects throttle and pedal position signals to:

If the signal is missing, erratic, implausible, or inconsistent with other inputs, the PCM may store P0120.

Unlike some more specific throttle-position codes, P0120 is a broad circuit-malfunction code.

It may indicate:

P0120 Quick Facts

ItemInformation
Diagnostic CodeP0120
Generic DefinitionThrottle/Pedal Position Sensor/Switch “A” Circuit Malfunction
SystemFuel, throttle, and electronic engine control
Fault TypeElectrical circuit or sensor-performance fault
Common SymptomsReduced power, poor throttle response, rough idle, stalling
Common CausesSensor failure, wiring damage, connector faults, reference-voltage problems
SeverityModerate to high
Safe to Drive?Usually not recommended
Typical Repair Cost$100–$1,200+
Related CodesP0121, P0122, P0123, P0124, P0220, P2135

What Is the Throttle Position Sensor?

The Throttle Position Sensor measures the angle of the throttle plate.

The PCM uses this information to determine:

On cable-operated throttle bodies, the TPS is usually connected directly to the throttle shaft.

As the throttle opens, the sensor signal changes.

On many older vehicles, a typical signal may rise from approximately:

Exact values vary by manufacturer.

The important feature is that the signal must change smoothly and remain within specification.

What Is the Accelerator Pedal Position Sensor?

Drive-by-wire vehicles do not use a direct throttle cable.

Instead, the accelerator pedal contains one or more position sensors.

When the driver presses the pedal:

  1. The pedal sensor sends a request to the PCM.
  2. The PCM evaluates the signal.
  3. The PCM commands the throttle motor.
  4. Throttle-position sensors confirm that the throttle plate moved correctly.

The PCM constantly compares pedal position with throttle position.

If one signal becomes unreliable, the system may enter reduced-power mode.

Why Does the Code Say Throttle/Pedal Position Sensor?

The generic P0120 description covers different designs.

Depending on the manufacturer, Sensor “A” may refer to:

Factory service information is necessary to confirm exactly which component the code references.

A generic scanner may display the same description across vehicles even though the actual diagnostic path differs.

What Does Sensor “A” Mean?

Many electronic throttle systems use redundant sensors.

For example, the throttle body may contain:

The accelerator pedal may contain:

These signals may:

Redundancy allows the PCM to detect a faulty signal before uncontrolled throttle movement occurs.

Sensor “A” generally identifies the primary circuit, but the exact configuration depends on the vehicle.

How the Throttle Position Sensor Works

Most throttle-position sensors operate using one of these designs:

Potentiometer-Type Sensor

A potentiometer uses a movable contact across a resistive track.

As the throttle shaft turns, signal voltage changes.

Wear in the track may create:

Hall-Effect Sensor

A Hall-effect sensor measures magnetic-field changes without direct electrical contact.

It generally offers better durability but can still fail because of:

How the PCM Uses the Throttle Signal

The PCM uses throttle and pedal data to control:

An incorrect throttle-position signal may affect several systems simultaneously.

How the PCM Detects P0120

The PCM may store P0120 when it detects:

The code may set immediately after startup or only while accelerating.

Common P0120 Scan-Tool Patterns

Pattern 1: Throttle Position Stuck at Zero

Possible causes:

Pattern 2: Throttle Position Stuck at 100 Percent

Possible causes:

Pattern 3: Throttle Position Jumps During Pedal Movement

Possible causes:

Pattern 4: Pedal Position Changes but Throttle Position Does Not

Possible causes:

Pattern 5: Sensor A and Sensor B Disagree

Possible causes:

Common Symptoms of P0120

Possible symptoms include:

Symptoms vary depending on whether the vehicle uses a mechanical throttle cable or electronic throttle control.

Check Engine Light

The Check Engine Light may appear alone or with:

Several systems may be disabled because they depend on accurate throttle-position information.

Reduced-Power Mode

Electronic throttle systems often enter a fail-safe mode when the PCM cannot trust the throttle or pedal signal.

The system may:

This protects against unintended throttle movement.

It also ensures the vehicle accelerates with all the urgency of a refrigerator being pushed uphill.

Poor Throttle Response

The engine may:

On some vehicles, cycling the ignition may temporarily restore normal operation.

That does not mean the fault repaired itself.

No Throttle Response

A serious circuit failure may cause the PCM to ignore the accelerator-pedal signal.

The engine may idle but refuse to accelerate.

Do not drive the vehicle in traffic if throttle response is unreliable.

Rough Idle

A faulty throttle-position signal can disrupt:

The engine may:

High Idle

A falsely elevated throttle-position signal may make the PCM believe the throttle is partially open.

Possible symptoms include:

On electronic throttle systems, the PCM may also command a fixed fail-safe throttle angle.

Stalling

The engine may stall:

A signal dropout may prevent the PCM from managing idle correctly.

Hard Starting or No Start

P0120 may contribute to:

Some PCMs interpret wide-open throttle during cranking as a request to disable or reduce fuel injection.

A false high throttle signal can therefore create a no-start condition.

Hesitation and Surging

If throttle position changes suddenly without actual pedal movement, the PCM may alter:

This may cause:

Poor Acceleration

The PCM may intentionally restrict engine torque.

The vehicle may:

Transmission Shift Problems

Throttle position is a major input for transmission control.

Possible symptoms include:

Transmission symptoms may be secondary to P0120 rather than evidence of an internal transmission problem.

Cruise Control Disabled

Cruise control usually requires reliable pedal and throttle signals.

P0120 may disable cruise control until the fault is repaired.

Traction and Stability Control Warnings

Traction and stability systems may request reduced engine torque through the electronic throttle.

If throttle control is unreliable, these systems may be disabled.

The dashboard may display several warnings from one underlying fault.

Poor Fuel Economy

Incorrect throttle data may affect:

The result may be increased fuel consumption.

Black Smoke

If the PCM receives incorrect load or throttle information, the engine may run rich.

Possible symptoms include:

Black smoke is possible but is not the most common P0120 symptom.

Is P0120 Serious?

P0120 should be considered a moderate-to-high severity code.

The problem may affect:

On electronic throttle-control vehicles, the PCM may enter reduced-power mode with little warning.

A vehicle that cannot accelerate predictably is unsafe in traffic.

Can You Drive With P0120?

Driving is generally not recommended until the fault is diagnosed.

A very short trip may be possible if:

Do not continue driving if:

Have the vehicle towed if throttle control is unpredictable.

Does P0120 Mean the Throttle Position Sensor Is Bad?

Not necessarily.

A failed sensor can cause P0120, but common alternatives include:

The circuit should be tested before parts are replaced.

Can a Dirty Throttle Body Cause P0120?

A dirty throttle body can contribute on electronic throttle-control vehicles.

Carbon buildup may cause:

However, P0120 is primarily a circuit-malfunction code.

A dirty throttle body should not be blamed without checking electrical data.

Can a Loose Connector Cause P0120?

Yes.

Loose connectors may cause:

Inspect connectors at:

Can Damaged Wiring Cause P0120?

Yes.

Common wiring failures include:

Wiring near the throttle body may be exposed to:

Can a Five-Volt Reference Problem Cause P0120?

Yes.

Many throttle and pedal sensors use a PCM-supplied five-volt reference.

If that circuit is:

P0120 and other sensor codes may appear.

Several sensors may malfunction simultaneously if they share the same reference circuit.

Can a Bad Ground Cause P0120?

Yes.

A poor sensor ground or low-reference circuit can distort the position signal.

Possible causes include:

Can the Accelerator Pedal Sensor Cause P0120?

Yes.

On some vehicles, P0120 refers to the accelerator-pedal position Sensor A circuit.

A faulty pedal assembly may cause:

The pedal sensor may not be serviceable separately from the pedal assembly.

Can a Failed Electronic Throttle Body Cause P0120?

Yes.

Electronic throttle bodies may contain:

Failure may require replacement of the complete throttle-body assembly.

Can a Sticking Throttle Plate Cause P0120?

A sticking throttle plate may contribute to position or correlation faults.

Common causes include:

Do not force an electronic throttle plate open unless the manufacturer permits it.

Some throttle bodies can be damaged by aggressive manual movement.

Can a Vacuum Leak Cause P0120?

A vacuum leak does not usually cause P0120 directly.

It may cause:

These symptoms may resemble a throttle-position fault, but the code itself points toward the sensor or circuit.

Can a Weak Battery Cause P0120?

Low system voltage may contribute to electronic throttle-control problems.

Check battery and charging voltage if P0120 appears with:

A weak battery is not the most common direct cause, but it can complicate diagnosis.

Can the PCM Cause P0120?

PCM failure is possible but uncommon.

Potential module-related problems include:

The PCM should be suspected only after the sensor, throttle body, pedal assembly, wiring, power, and grounds have been tested.

P0120 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
P0221Sensor B range/performance problem
P0222Sensor B circuit low input
P0223Sensor B circuit high input
P0224Sensor B circuit intermittent
P2135Throttle Position Sensors A/B voltage correlation

P0120 vs. P0121

P0120 is a general circuit-malfunction code.

P0121 means the signal exists but does not fall within the expected range or performance pattern.

P0120 vs. P0122

P0122 indicates that the Sensor A signal voltage is consistently too low.

Common causes include:

P0120 vs. P0123

P0123 indicates that the Sensor A signal voltage is consistently too high.

Common causes include:

P0120 vs. P0124

P0124 indicates that the Sensor A circuit is intermittent.

The signal may repeatedly drop out or spike.

P0120 vs. P2135

P2135 indicates that two throttle-position sensor signals do not correlate correctly.

P0120 is broader and may involve the primary Sensor A circuit itself.

25 Common Causes of P0120

The most common causes include:

  1. Failed throttle-position sensor
  2. Failed accelerator-pedal position sensor
  3. Failed electronic throttle body
  4. Dirty or sticking throttle plate
  5. Loose throttle-body connector
  6. Loose accelerator-pedal connector
  7. Broken connector lock
  8. Weak terminal tension
  9. Backed-out connector terminal
  10. Corroded terminals
  11. Water intrusion
  12. Oil contamination
  13. Open signal wire
  14. Signal wire shorted to ground
  15. Signal wire shorted to voltage
  16. Missing five-volt reference
  17. Five-volt reference shorted by another sensor
  18. Poor sensor ground
  19. Shared low-reference problem
  20. Harness damage near the throttle body
  21. Harness damage near the accelerator pedal
  22. Failed previous wiring repair
  23. Incorrectly adjusted TPS
  24. PCM connector problem
  25. PCM failure or software issue

1. Failed Throttle-Position Sensor

A worn or damaged TPS may produce:

Older potentiometer-style sensors are especially vulnerable to wear.

2. Failed Accelerator-Pedal Position Sensor

The pedal sensor may become:

Many pedal sensors are sold only with the complete pedal assembly.

3. Failed Electronic Throttle Body

An electronic throttle body may fail because of:

4. Dirty or Sticking Throttle Plate

Deposits around the throttle plate may cause:

Cleaning may help if the component is mechanically sound.

5. Loose Throttle-Body Connector

Engine vibration and heat may loosen or damage the connector.

The circuit may fail during:

6. Loose Accelerator-Pedal Connector

The pedal connector may be disturbed by:

7. Broken Connector Lock

A connector with a broken lock may appear attached while making unreliable contact.

Replace the connector housing or pigtail when necessary.

8. Weak Terminal Tension

Weak terminals may lose contact with sensor pins.

A circuit can pass a stationary voltage test and still fail during vibration.

9. Backed-Out Terminal

A terminal may retreat into the connector housing when the connector is installed.

Inspect pin depth carefully.

10. Corroded Terminals

Corrosion can create:

11. Water Intrusion

Water may enter through:

12. Oil Contamination

Oil may soften seals, attract debris, and damage connector integrity.

Find and repair the source of contamination.

13. Open Signal Wire

A broken signal wire prevents the PCM from receiving accurate position data.

The wire may be broken internally while the insulation remains intact.

14. Signal Wire Shorted to Ground

A short to ground may force the signal low and trigger P0120 or P0122.

15. Signal Wire Shorted to Voltage

A short to voltage may force the signal high and trigger P0120 or P0123.

16. Missing Five-Volt Reference

The sensor cannot operate normally without its reference supply.

Possible causes include:

17. Five-Volt Reference Shorted by Another Sensor

A failed sensor elsewhere may pull the entire five-volt circuit low.

Possible shared sensors include:

Unplugging sensors one at a time may help isolate the fault when factory procedures permit.

18. Poor Sensor Ground

A high-resistance ground can distort the position signal.

Voltage-drop testing under load is more useful than continuity alone.

19. Shared Low-Reference Problem

Several sensors may use the same ground circuit.

Multiple implausible sensor readings suggest a shared fault.

20. Harness Damage Near the Throttle Body

Inspect for:

21. Harness Damage Near the Accelerator Pedal

Inspect for:

22. Failed Previous Wiring Repair

Poor repairs may include:

23. Incorrectly Adjusted TPS

Some older throttle-position sensors are adjustable.

Incorrect installation may produce:

Most modern sensors are not adjustable.

24. PCM Connector Problem

Inspect for:

25. PCM Failure or Software Issue

Module failure is rare.

Check technical service bulletins and software updates before replacing the PCM.

Most Likely Causes by Symptom

SymptomMost Likely Causes
Reduced-power modeThrottle body, pedal sensor, wiring, correlation issue
No throttle responsePedal sensor, throttle body, reference voltage
High idleTPS bias, dirty throttle body, vacuum leak
Code appears after throttle cleaningConnector loose, throttle adaptation needed
Several sensors have low voltageShared five-volt reference short
Signal stuck at zeroOpen circuit, missing reference, failed sensor
Signal stuck at 100%Short to voltage, open ground, failed sensor
Signal jumps during movementWorn TPS, connector fault, broken wire
Code appears after interior workPedal connector or wiring damage
Code appears after engine repairThrottle connector or harness disturbance

Common Vehicles Affected by P0120

P0120 is a generic code that may appear on most 1996-and-newer vehicles, including models from:

The exact meaning of Sensor A varies by manufacturer and model.

P0120 and Electronic Throttle Fail-Safe Mode

When throttle data becomes unreliable, the PCM may use a fail-safe strategy.

Depending on the fault, it may:

Fail-safe operation may disappear after restarting the engine but return when the fault is detected again.

P0120 and Throttle Relearn Procedures

Some vehicles require a throttle or idle relearn after:

A missing relearn does not always cause P0120, but it may create:

Follow manufacturer procedures.

P0120 and Throttle-Body Cleaning

Throttle-body cleaning may help when carbon buildup causes mechanical binding.

However:

P0120 and Five-Volt Reference Codes

If P0120 appears with several unrelated sensor codes, suspect a shared reference-voltage problem.

Look for codes involving:

One failed sensor can pull down the entire circuit.

P0120 and Transmission Problems

Throttle-position data helps determine transmission load.

Before replacing transmission components for harsh or delayed shifting, repair P0120 and verify whether shifting returns to normal.

P0120 and Emissions Testing

A vehicle with P0120 will usually fail an emissions inspection because:

Clearing the code without repairing the fault resets monitors and rarely solves anything.

Can P0120 Clear Itself?

The warning light may turn off after several fault-free drive cycles.

However:

Throttle-control faults should be diagnosed even if the light temporarily turns off.

Final Thoughts

The P0120 Throttle/Pedal Position Sensor “A” Circuit Malfunction code means the PCM has detected an electrical or performance problem in the primary throttle or accelerator-pedal position circuit.

The fault may involve:

Common symptoms include:

The most common causes are:

P0120 should not be diagnosed by throwing a throttle body at the vehicle and hoping the Check Engine Light appreciates the gesture.

The correct approach is to identify which Sensor A circuit the vehicle uses, examine live data, inspect the connectors, verify the five-volt reference and ground, and test the signal through the entire throttle or pedal range.

How to Diagnose the P0120 Code

Diagnosing P0120 requires identifying which Throttle/Pedal Position Sensor “A” circuit the vehicle uses and then proving whether the problem comes from the sensor, electronic throttle body, accelerator-pedal assembly, wiring, reference voltage, ground, or PCM input.

Because P0120 is a broad circuit-malfunction code, the diagnostic process should not begin with parts replacement.

On one vehicle, Sensor “A” may refer to a serviceable throttle-position sensor mounted on a cable-operated throttle body.

On another vehicle, the same code may involve:

Before touching the throttle body, confirm the exact circuit definition in the manufacturer’s service information.

That step prevents the surprisingly common diagnostic strategy of replacing an expensive throttle body because a generic scanner displayed the word “throttle.”

P0120 Safety Warning

Electronic throttle-control systems are safety-critical.

Before beginning diagnosis:

Electronic throttle motors can move unexpectedly when:

A throttle plate is not especially large, but it is more than capable of turning a casual finger placement into a memorable lesson.

Tools Needed to Diagnose P0120

A complete diagnosis may require:

An oscilloscope is especially useful when the sensor signal contains brief dropouts or noise that a scan tool refresh rate may miss.

Step 1: Confirm the P0120 Code

Connect the scan tool and record:

Do not erase the code before recording freeze-frame data.

Freeze-frame information may reveal whether the fault occurred:

Step 2: Check for Related Trouble Codes

Look for codes involving:

Common related codes include:

The related codes often determine where diagnosis should begin.

For example:

Related Code PatternLikely Direction
P0120 onlySensor A circuit, connector, wiring, or component
P0120 with P0122Low signal, short to ground, lost reference
P0120 with P0123High signal, open ground, short to voltage
P0120 with P0124Intermittent connection or sensor dropout
P0120 with P2135Throttle Sensor A/B correlation problem
P0120 with several five-volt sensor codesShared reference-voltage fault
P0120 with pedal-position codesAccelerator-pedal circuit or shared wiring
P0120 with throttle-actuator codesElectronic throttle body or motor-control fault

Step 3: Identify What Sensor “A” Means

Use the factory wiring diagram and diagnostic description to determine whether Sensor “A” refers to:

Do not assume Sensor “A” is located at the throttle body.

On some vehicles, the generic description mentions both throttle and pedal position even though the manufacturer assigns P0120 to one specific circuit.

Record:

Step 4: Inspect the Battery and Charging System

Electronic throttle systems depend on stable voltage.

Check battery voltage with the engine off.

A fully charged battery will commonly measure approximately:

During cranking, voltage should not collapse below the manufacturer’s specification.

With the engine running, charging voltage commonly falls near:

Exact specifications vary.

Inspect for:

Use a charger or maintainer during extended ignition-on testing.

Low battery voltage can create misleading electronic throttle faults and may interrupt relearn procedures.

Step 5: Perform a Visual Inspection

Inspect the complete system before testing individual wires.

Check:

Look for:

A connector that is slightly loose can create a P0120 fault without looking dramatically damaged.

Step 6: Inspect the Throttle-Body Connector

Disconnect the throttle-body connector with the ignition off.

Inspect for:

Check whether the connector fits securely and locks into place.

A broken retaining clip can allow vibration to interrupt the signal.

Do not rely on the connector merely appearing seated.

Step 7: Inspect the Accelerator-Pedal Connector

The accelerator-pedal connector may be exposed to:

Inspect the connector and harness near the pedal bracket.

Make sure the harness is not:

Step 8: Inspect the Throttle Plate

With the ignition off, inspect the throttle bore for:

Do not force the throttle plate unless service information permits manual movement.

Some electronic throttle bodies allow gentle movement with the ignition off. Others may be damaged by aggressive handling.

If carbon deposits are severe, clean the throttle body according to the manufacturer’s instructions.

Do not assume cleaning alone will correct P0120. The code still requires electrical verification.

Step 9: Check Scan-Tool Throttle Position at Rest

Turn the ignition on with the engine off.

Observe:

At rest, values should remain stable.

Depending on the scan tool, closed-throttle position may display as:

Do not expect every vehicle to display exactly zero.

The important questions are:

Step 10: Slowly Press the Accelerator Pedal

With the ignition on and engine off, slowly press the accelerator pedal from rest to full travel.

Watch the graph for:

Repeat the test several times.

Move the pedal:

Worn sensors often fail at the positions used most frequently during normal driving.

Step 11: Graph Throttle and Pedal Signals Together

Graph the following PIDs simultaneously when possible:

A normal system should show a consistent relationship between:

  1. Pedal movement
  2. PCM throttle command
  3. Actual throttle movement
  4. Redundant position signals

An abnormal pattern may reveal the fault.

Pedal Moves but Commanded Throttle Does Not

Possible causes include:

Commanded Throttle Moves but Actual Throttle Does Not

Possible causes include:

Actual Throttle Moves but Sensor A Drops Out

Possible causes include:

Sensor A and Sensor B Disagree

Possible causes include:

Step 12: Check Sensor A Voltage

Backprobe the Sensor A signal circuit according to the wiring diagram.

Many position sensors produce a signal somewhere between approximately:

These are general examples, not universal specifications.

Some redundant sensors:

Compare actual readings with factory specifications.

Step 13: Sweep-Test the Signal

Move the throttle or pedal slowly through its full travel while monitoring voltage.

A healthy analog signal should change smoothly.

Watch for:

A digital multimeter may not display very brief glitches.

Use an oscilloscope when the scan tool or meter shows no fault but the code continues to return.

Step 14: Use an Oscilloscope

Connect the oscilloscope to Sensor A signal and ground.

Perform a slow sweep.

A healthy signal should appear as a smooth ramp.

An unhealthy signal may show:

Repeat the test while:

The oscilloscope may capture faults lasting only a few milliseconds.

Step 15: Perform a Wiggle Test

Monitor live data or oscilloscope voltage while moving:

Do not pull hard enough to create a new fault.

Watch for:

If the signal changes when a specific section is moved, inspect that area closely for:

Step 16: Test Terminal Tension

Use the correct terminal test probe.

Do not insert oversized meter leads into the connector because they can spread the terminals and create the problem you are attempting to diagnose.

Compare suspect terminals with known-good terminals of the same design.

Replace terminals that:

Step 17: Verify the Five-Volt Reference

With the ignition on, measure the reference-voltage circuit.

A typical value is near five volts, but use manufacturer specifications.

Possible results include:

Correct Reference Voltage

The problem may remain in:

Zero Volts

Possible causes include:

Low Reference Voltage

Possible causes include:

Battery Voltage on the Reference Circuit

Possible causes include:

Never supply battery voltage to the five-volt reference circuit.

Step 18: Check for a Shared Five-Volt Reference Fault

Review the wiring diagram to identify sensors sharing the same reference supply.

Possible shared sensors include:

If the five-volt reference is low, disconnect shared sensors one at a time when permitted by factory procedures.

If the reference returns to normal after one sensor is disconnected, that sensor or its wiring may be pulling down the circuit.

Do not overlook harness shorts between branches of the shared reference circuit.

Step 19: Test the Sensor Ground

Measure the low-reference or sensor-ground circuit.

A ground can show continuity and still fail under load.

Perform a voltage-drop test between:

The voltage drop should remain within the manufacturer’s specification.

Excessive voltage drop may indicate:

Step 20: Test the Signal Circuit for an Open

Disconnect the sensor and PCM as required.

Measure resistance from the sensor signal terminal to the PCM input terminal.

The wire should have very low resistance.

Flex and move the harness during testing.

An internally broken conductor may pass a stationary continuity test and fail when bent.

Step 21: Test the Signal Circuit for a Short to Ground

With both ends disconnected, measure resistance between the signal wire and ground.

The circuit should not show unintended continuity.

Inspect areas where the harness contacts:

Step 22: Test the Signal Circuit for a Short to Voltage

Check whether the signal wire has continuity to:

Harness damage can cause adjacent wires to contact each other intermittently.

Step 23: Load-Test the Wiring

A circuit may pass resistance testing but fail when current flows.

Use a manufacturer-approved load test to verify:

A test light or resistor may be used only when appropriate for the circuit.

Never use a high-current incandescent test light on a low-current PCM signal unless the service procedure specifically permits it.

Step 24: Check Throttle Position Sensor Resistance

This step applies mainly to older serviceable potentiometer-style sensors.

Disconnect the sensor and measure resistance across the specified terminals.

Move the throttle slowly.

Resistance should change smoothly.

Look for:

Do not use resistance testing on Hall-effect or internally powered electronic sensors unless the service procedure instructs it.

Step 25: Check Closed-Throttle Voltage

Older adjustable throttle-position sensors may require a specified closed-throttle voltage.

If the voltage is incorrect, inspect for:

Adjust only when the manufacturer provides a procedure.

Most modern throttle-position sensors are not adjustable.

Step 26: Check Wide-Open-Throttle Voltage

Move the throttle to the fully open position when permitted.

Verify that voltage reaches the expected range without:

A sensor may work near idle but fail near wide-open throttle.

Step 27: Test the Accelerator-Pedal Position Sensor

On drive-by-wire vehicles, graph both pedal signals.

The pedal assembly may use:

Compare the signals throughout pedal travel.

Possible faults include:

Many pedal assemblies are replaced as a complete unit.

Step 28: Check Pedal Movement

Inspect the accelerator pedal for:

Confirm that the pedal returns fully when released.

A physically obstructed pedal can create implausible position data even when the electronics function normally.

Step 29: Test the Electronic Throttle Motor

If the code appears with throttle-actuator faults, test the motor circuit according to factory procedures.

Possible checks include:

Do not apply power directly unless the manufacturer specifically provides a safe procedure.

The throttle motor may draw excessive current if:

Step 30: Perform a Bidirectional Throttle Test

A manufacturer-capable scan tool may allow the throttle plate to be commanded through a controlled range.

Compare:

Possible patterns include:

Command Changes but Throttle Does Not Move

Suspect:

Throttle Moves but Position Feedback Is Wrong

Suspect:

Movement Is Slow or Uneven

Suspect:

Step 31: Compare Throttle Position With MAP and MAF Data

Throttle opening should generally correspond with changes in:

If throttle position reports wide open while airflow and engine load remain near idle, the position signal is implausible.

If pedal position rises but throttle angle remains fixed, the system may be in fail-safe mode or the throttle body may not be responding.

These comparisons help distinguish a faulty signal from actual throttle movement.

Step 32: Check for Intake Restrictions and Air Leaks

Vacuum leaks do not normally cause P0120 directly, but they may complicate symptoms.

Inspect for:

Aftermarket intake systems may place tension on the throttle-body connector or harness.

Step 33: Inspect Aftermarket Wiring

Inspect installations involving:

Pedal controllers installed between the accelerator pedal and factory harness can directly affect position signals.

Remove or bypass aftermarket devices according to the manufacturer’s procedures before continuing diagnosis.

Step 34: Review Recent Repairs

P0120 may appear after:

Check whether:

Step 35: Check for Technical Service Bulletins

Search manufacturer service information for bulletins involving:

A bulletin may save hours of diagnosis and prevent replacement of a component that the manufacturer already knows is not the root cause.

Step 36: Check PCM Power and Grounds

Before condemning the PCM, verify:

A weak PCM ground can affect several sensor signals simultaneously.

Step 37: Verify the Signal at the PCM

If the signal is correct at the sensor but incorrect on scan data, measure the signal at the PCM terminal.

Possible results include:

Correct at Sensor and Correct at PCM

Suspect:

Correct at Sensor but Incorrect at PCM

Suspect:

Incorrect at Sensor

Suspect:

Step 38: Consider PCM Software

Some vehicles may require:

Programming should only be performed with:

Do not use software updates as a substitute for electrical testing.

Step 39: Consider PCM Failure

PCM failure is rare.

Only suspect the PCM after confirming:

Module replacement may require:

How to Fix the P0120 Code

The correct repair depends on the confirmed failure.

Common P0120 repairs include:

Do not replace the throttle body unless testing confirms that it contains the failed sensor, motor, or internal electronics.

Throttle-Body Cleaning Procedure

Use only a cleaner approved for throttle bodies.

A general procedure may include:

  1. Turn the ignition off.
  2. Remove the intake duct.
  3. Inspect the throttle bore.
  4. Apply cleaner to a clean cloth rather than flooding the electronics.
  5. Remove deposits from the bore and plate.
  6. Avoid damaging protective coatings.
  7. Reinstall the intake duct securely.
  8. Perform the required throttle or idle relearn.
  9. Clear codes and retest.

Follow vehicle-specific instructions.

Some manufacturers warn against manually opening the electronic throttle plate.

Throttle Position Sensor Replacement

This applies only when the sensor is available separately.

A general procedure may include:

  1. Disconnect the battery when required.
  2. Disconnect the TPS connector.
  3. Mark the original sensor position if adjustable.
  4. Remove the retaining screws.
  5. Remove the sensor carefully from the throttle shaft.
  6. Install the replacement in the correct orientation.
  7. Set closed-throttle voltage when adjustment is required.
  8. Tighten fasteners to specification.
  9. Reconnect the connector.
  10. Perform relearn or calibration.
  11. Verify live data.

Do not attempt to replace an internal sensor that is permanently integrated into an electronic throttle body.

Electronic Throttle-Body Replacement

A general replacement procedure may include:

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

Do not reuse damaged gaskets.

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 the pedal mounting fasteners.
  5. Remove the assembly.
  6. Install the replacement pedal.
  7. Tighten fasteners to specification.
  8. Reconnect the connector.
  9. Confirm unobstructed pedal travel.
  10. Perform calibration or relearn when required.
  11. Verify both pedal-position signals.

Make sure the floor mat does not interfere with pedal movement after installation.

Connector Repair

Replace the connector or pigtail when it has:

A proper connector repair should use:

Stagger wire splices when possible to avoid creating a rigid bulge in the harness.

Wiring Repair

Remove all damaged or corroded wire.

Do not splice into green or blackened copper.

Use:

Keep repaired wiring away from:

Five-Volt Reference Repair

If another sensor is pulling down the reference circuit:

  1. Identify all shared sensors.
  2. Disconnect each branch according to service information.
  3. Observe whether reference voltage returns.
  4. Inspect the failed branch for a short.
  5. Repair wiring or replace the failed sensor.
  6. Confirm all shared sensor readings return to normal.

A shared five-volt fault may generate several unrelated codes at once.

Replacing every sensor listed by the scanner is not diagnosis. It is an expensive group project.

Ground Circuit Repair

Repair poor grounds by:

Confirm the repair with a loaded voltage-drop test.

Throttle Relearn Procedures

A throttle or idle relearn may be required after:

Relearn methods vary widely.

They may involve:

Always use the manufacturer’s procedure.

A generic online pedal dance may work on one model and waste 20 minutes on another.

Common Throttle Relearn Conditions

The procedure may require:

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

How to Verify the P0120 Repair

After completing repairs:

  1. Clear stored codes.
  2. Turn the ignition off for the specified period.
  3. Perform the required relearn.
  4. Start the engine.
  5. Confirm stable idle.
  6. Check throttle and pedal live data.
  7. Slowly sweep the accelerator pedal.
  8. Verify smooth Sensor A and Sensor B signals.
  9. Confirm commanded and actual throttle angles agree.
  10. Perform a road test.
  11. Recheck pending codes.
  12. Confirm reduced-power mode does not return.
  13. Verify transmission shifting.
  14. Confirm cruise and traction systems operate normally.
  15. Confirm readiness monitors begin completing.

The repair is not verified merely because the Check Engine Light stays off during a two-minute idle test.

Recommended Road-Test Procedure

When safe and legal, include:

Monitor:

Stop the road test if throttle response becomes unreliable.

Common Scan-Tool Patterns and Likely Causes

Scan-Tool PatternLikely Cause
Sensor A fixed at 0%Open signal, missing reference, failed sensor
Sensor A fixed at 100%Short to voltage, open ground, failed sensor
Sensor A jumps during movementWorn sensor, loose connector, broken wire
Pedal signal moves but throttle command does notPedal circuit fault or fail-safe mode
Commanded throttle changes but actual does notThrottle motor, binding plate, internal gears
Sensor A and B disagree throughout travelThrottle body or pedal assembly fault
Several five-volt sensors read lowShared reference circuit pulled down
Signal changes when harness movesConnector or wiring fault
Code returns only when hotHeat-sensitive sensor or terminal fault
Code appears after battery disconnectRelearn needed or low-voltage event
Throttle angle correct but scan signal wrongSignal circuit or PCM input issue
Throttle angle sticks near one positionMechanical binding or internal throttle-body fault

P0120 Repair Cost

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

RepairTypical Cost
Diagnostic testing$100–$250
Throttle-body cleaning$100–$250
Connector repair$100–$400
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+
Ground repair$100–$350
PCM software update$100–$300
PCM replacement and programming$1,000–$3,000+

These figures are general estimates.

Luxury vehicles, turbocharged engines, and throttle bodies with integrated cooling or intake components may cost more.

Can You Fix P0120 Yourself?

A careful DIY owner may be able to:

Professional diagnosis may be better when:

Throttle-control diagnosis is not the best place to guess with jumper wires.

Common P0120 Diagnostic Mistakes

Replacing the Throttle Body Without Testing

The throttle body is expensive and may not be the failed component.

The actual problem may be:

Assuming Sensor A Is Always the TPS

Sensor A may refer to the accelerator-pedal circuit.

Confirm the manufacturer definition.

Ignoring Related Codes

Correlation, reference-voltage, and pedal-position codes can identify the correct diagnostic path.

Cleaning the Throttle Body and Declaring Victory

Cleaning may correct mechanical binding but will not repair:

Forcing the Electronic Throttle Plate

Aggressive manual movement can damage:

Using a Test Light on Sensor Circuits

A high-current test light can damage low-current PCM circuits.

Use the correct meter or approved load.

Checking Continuity Without Loading the Circuit

A corroded or partially broken wire may show continuity but fail in operation.

Use voltage-drop or load testing.

Overlooking Shared Five-Volt Circuits

A failed pressure sensor elsewhere can pull down the throttle reference circuit.

Forgetting Pedal Controllers

Aftermarket throttle boosters can create pedal signal faults and correlation codes.

Ignoring Terminal Tension

A terminal may look clean and still fit too loosely.

Skipping the Relearn Procedure

A new or cleaned throttle body may require calibration before normal operation returns.

Condemning the PCM Too Early

PCM failure is rare compared with connector, sensor, and wiring faults.

Manufacturer-Specific P0120 Notes

General Motors

GM vehicles may display a Reduced Engine Power warning when throttle or pedal signals become unreliable.

Inspect:

Some applications require throttle-body replacement because the position sensors are internal.

Ford and Lincoln

Ford electronic throttle systems may use detailed correlation and actuator codes alongside P0120.

Inspect:

Use Ford-capable scan data to compare desired and actual throttle angle.

Toyota and Lexus

Toyota systems may identify throttle and pedal position signals separately in enhanced data.

Graph:

Perform the specified initialization procedure after component replacement when required.

Honda and Acura

Honda systems may enter fail-safe operation when pedal or throttle signals disagree.

Inspect:

Use OEM-quality components because incorrect aftermarket signal scaling can cause repeat faults.

Nissan and Infiniti

Nissan vehicles may require:

The exact procedures depend on the model and repair performed.

Failure to complete required learning procedures may cause idle or throttle complaints after replacement.

Hyundai and Kia

Inspect:

Use enhanced data to compare redundant channels.

Volkswagen and Audi

Electronic throttle systems may require basic settings after:

Inspect connector terminals and verify adaptation completes successfully.

BMW and MINI

BMW systems may refer to throttle, pedal, or plausibility faults using manufacturer-specific descriptions.

Use BMW-capable diagnostics to examine:

Generic P0120 wording may not provide enough detail for accurate diagnosis.

Mercedes-Benz

Mercedes electronic throttle systems may integrate throttle and pedal plausibility monitoring across several modules.

Inspect:

Manufacturer diagnostics are strongly recommended.

Subaru

Inspect:

Throttle-body replacement or cleaning may require an idle relearn period.

Chrysler, Dodge, Jeep and Ram

An electronic throttle-control warning light may accompany P0120.

Inspect:

Some vehicles may enter severe throttle limitation until the ignition is cycled.

Preventing Future P0120 Problems

Reduce the likelihood of future faults by:

Frequently Asked Questions About P0120 Diagnosis and Repair

How do you diagnose P0120?

Begin by confirming whether Sensor A refers to the throttle body or accelerator pedal. Then inspect the connectors, graph live data, verify the five-volt reference and ground, sweep-test the signal, compare redundant sensors, and check the wiring between the component and PCM.

What is the most common fix for P0120?

Common repairs include fixing a loose connector, repairing damaged wiring, replacing a failed TPS, replacing the accelerator-pedal assembly, or replacing an electronic throttle body with an internal sensor failure.

Can cleaning the throttle body fix P0120?

Cleaning may help if carbon buildup causes mechanical binding or an incorrect closed-throttle position. It will not repair a failed sensor, broken wire, loose terminal, or missing reference voltage.

How do I test a throttle-position sensor?

Measure signal voltage while slowly moving the throttle through its full range. The voltage should change smoothly without dropouts, spikes, or dead spots. Compare the results with factory specifications.

What voltage should a TPS have?

Many analog sensors produce roughly 0.3–1.0 volts at closed throttle and 4.0–4.8 volts at wide-open throttle. Exact specifications and signal direction vary by vehicle.

Can a bad accelerator-pedal sensor cause P0120?

Yes. On some vehicles, Sensor A refers to the primary accelerator-pedal position circuit.

Can a bad throttle body cause P0120?

Yes. Electronic throttle bodies often contain internal position sensors that are not serviceable separately.

Can a shared five-volt reference cause P0120?

Yes. A failed sensor elsewhere can pull down the reference voltage shared with the throttle or pedal sensor.

How do I know whether the pedal or throttle body is bad?

Graph pedal position, commanded throttle angle, and actual throttle angle together. If pedal data is wrong, suspect the pedal circuit. If pedal and command data are correct but actual throttle position is wrong, suspect the throttle body or its wiring.

Can low battery voltage cause P0120?

Low voltage can interfere with electronic throttle operation and calibration, especially when other low-voltage or communication codes are present.

Does a new throttle body need programming?

Some vehicles require programming, initialization, adaptation, or throttle relearn. Others only require an idle relearn. Follow model-specific service information.

Can I drive after replacing the throttle body without a relearn?

The engine may idle poorly, enter reduced-power mode, or store additional codes. Complete the required relearn before normal driving.

Why does P0120 return only during acceleration?

The sensor may have a worn section or wiring may move under engine torque. Graph the signal while duplicating the condition.

Why does P0120 appear after throttle-body cleaning?

The connector may be loose, the throttle plate may have been forced, cleaner may have entered the electronics, or the system may require relearn.

Can a vacuum leak cause P0120?

A vacuum leak usually does not directly trigger P0120, although it may cause high idle or drivability symptoms that resemble a throttle fault.

Can a bad MAP sensor cause P0120?

A failed MAP sensor may trigger P0120 indirectly if it shorts a five-volt reference circuit shared with the throttle or pedal sensor.

Can an aftermarket pedal controller cause P0120?

Yes. Pedal controllers alter or intercept accelerator-pedal signals and can produce circuit or correlation faults.

Is an oscilloscope necessary?

Not always, but it is valuable for finding brief signal dropouts, electrical noise, or intermittent faults that a multimeter may miss.

Can I replace only the throttle-position sensor?

Only if the manufacturer sells it separately and provides an adjustment or installation procedure. Many electronic throttle bodies require complete assembly replacement.

How long does P0120 diagnosis take?

A straightforward connector or sensor fault may be found quickly. Intermittent wiring, shared reference, or correlation faults can require several hours of testing.

How much does it cost to fix P0120?

Repairs may cost around $100–$350 for a serviceable sensor or connector repair, $150–$600 for a pedal assembly, and $300–$1,200 or more for an electronic throttle body. Extensive harness or PCM repairs cost more.

Will disconnecting the battery clear P0120?

It may erase some stored information temporarily, but it will not repair the fault. Battery disconnection may also erase throttle or idle adaptations.

Can P0120 cause transmission problems?

Yes. Throttle-position data affects transmission load calculations, shift timing, and torque management. Repair P0120 before assuming the transmission has an internal failure.

Can P0120 cause a no-start?

Yes. A falsely high throttle signal during cranking may activate clear-flood mode on some vehicles, reducing or disabling fuel injection.

Why does the engine only idle with P0120?

The PCM may intentionally limit the throttle to a fixed fail-safe position because it cannot trust the sensor data.

Can P0120 damage the catalytic converter?

Indirectly, yes. Incorrect throttle data may contribute to rich operation, misfires, and excessive exhaust heat.

Can P0120 turn off traction control?

Yes. Traction and stability systems may be disabled because they depend on reliable electronic throttle control.

What should I check first for P0120?

Begin with the related codes, factory code definition, battery voltage, throttle and pedal connectors, live position data, and the five-volt reference circuit.

Final Thoughts

The P0120 Throttle/Pedal Position Sensor “A” Circuit Malfunction code should be diagnosed as a complete electrical and electronic throttle-control system fault—not as an automatic request to replace the throttle body.

The correct diagnostic process begins by confirming exactly what Sensor A represents on the vehicle.

From there, test:

The most important live-data comparison is the relationship between what the driver requests, what the PCM commands, and what the throttle body actually does.

If the pedal signal changes correctly but the PCM does not command throttle movement, focus on the pedal input, fail-safe logic, or PCM processing.

If the PCM commands movement but the throttle plate does not respond, focus on the electronic throttle body, motor circuit, mechanical binding, or internal gears.

If the throttle moves correctly but Sensor A reports nonsense, focus on the position sensor, signal wire, connector, reference voltage, and ground.

P0120 may ultimately require a new throttle body, pedal assembly, or sensor. But those components should earn their replacement through testing.

Expensive parts do not become more accurate diagnostic tools simply because they arrive in attractive boxes.

Related Pro Street Diagnostic Guides

Throttle/Pedal Position Sensor A Codes

Complete OBD-II Code Libraries

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