P0120 Throttle or pedal position sensor A signal outside its normal range

Throttle position sensor / switch A circuit malfunction

P0120 in short

P0120 means the computer sees a throttle or pedal position sensor signal that is out of range or does not make sense. Common causes are a worn sensor, a damaged connector or wiring, or a dirty throttle body. The car may drop into reduced power, so get it checked soon.

The engine computer reads one or more position sensors on the throttle or accelerator pedal to know how much power you want. P0120 is set when circuit A of that sensor reports a voltage outside what the computer expects, or disagrees with the other sensor signal.

Because the throttle is electronically controlled on most cars built after the early 2000s, the computer protects itself by limiting engine power when it cannot trust the signal. GM bulletins for 2003 trucks describe a light and a reduced-power mode with this code, and say the problem is usually intermittent.

Older Nissan and Infiniti bulletins show the code can also be stored with no driveability complaint at all. What it means for you depends on whether the car is actually losing power.

Most likely causes

  1. Worn or failing throttle or pedal position sensor

    Common general cause
    Why it ranks here
    Reference pages for P0120 list the position sensor itself as the first suspect because its track wears and gives dropouts, which matches the intermittent behaviour GM describes.
    What would change this
    Rises if the scan-tool throttle reading jumps or drops out when you move the pedal slowly. Falls if the reading sweeps smoothly.
    How to test the accelerator pedal position sensor

  2. Damaged wiring or a loose, corroded connector at the sensor

    Common general cause
    Why it ranks here
    An open, short or high resistance in the sensor circuit gives the same out-of-range signal as a bad sensor, and is cheaper to check first.
    What would change this
    Rises if wiggling the harness or connector changes the reading. Falls if the wiring tests clean.

  3. Dirty or faulty throttle body

    Possible — needs testing
    Why it ranks here
    Reference pages list the throttle body as a possible cause when the sensor is built into it, but the evidence is general rather than tied to a vehicle.
    What would change this
    Rises if the plate is gummed up or the sensor is part of the throttle assembly and fails the test. Falls if the throttle moves freely and readings are smooth.
    How to test the electronic throttle body

  4. Intermittent fault on 2003 GM trucks (bulletins 3040 to 3042)

    Supported by vehicle data
    Why it ranks here
    GM published bulletins for 2003 Silverado, Sierra, Yukon, Tahoe, Suburban, Trailblazer and Envoy with this code set, but the NHTSA summary does not say what the repair is.
    What would change this
    Rises if you have one of those trucks and the code is intermittent. Falls on other vehicles.
    How to test the engine control module (ecm / pcm)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes and freeze-frame data. Note whether P0220, P0121, P0122 or P0123 are stored with P0120.

    Low riskTool: OBD-II scan tool

    • IfOther throttle or pedal codes are stored with it

      It meansA shared circuit, connector or 5-volt reference fault is likely.

      Go to step 3

    • IfP0120 is the only code

      It meansCheck the sensor reading next.

      Go to step 2

  2. With the key on and engine off, watch the throttle or pedal position reading on a scan tool while pressing the pedal slowly from rest to full.

    Low riskTool: scan tool with live data

  3. Inspect the sensor connector and harness for damage, then gently wiggle them with live data open.

    Low riskTool: scan tool with live data

Symptoms

  • Check engine light on, sometimes with a reduced-power or wrench light
  • Poor or delayed acceleration, hesitation
  • Rough or unsteady idle
  • Engine stalls or power drops away in traffic Gets more serious: stop and have it checked.

Compare with: Check engine light with loss of power

How to fix

  1. With the engine off, check the sensor connector for loose, bent or corroded pins and reseat it.

  2. Ask a dealer whether your VIN has a bulletin or software update for throttle or pedal codes.

Parts and cost context

  • Accelerator pedal position sensor:The pedal sensor is often part of the pedal assembly. Confirm with live data before buying one.
  • Electronic throttle body:On many cars the throttle position sensor is inside the throttle body. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2003 · Silverado 1500

    Supported by vehicle data

    GM bulletin 3040 covers 2003 Silverado, Avalanche and Suburban with a light and/or reduced engine power with P0120 set. GM calls it normally very intermittent. Whether it is still current is not verified.

  • 3040Status unverified

    Service engine soon light or reduced engine power with P0120, P0220, P1516, P1518

    2003silverado-1500, avalanche, suburban · issued · NHTSA 10009377

    Covers a Service Engine Soon light and/or reduced engine power mode on 2003 trucks that set P0120, P0220, P1516 or P1518. GM notes the condition is normally very intermittent.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 2003 · Sierra 1500

    Supported by vehicle data

    GM bulletin 3042 covers the 2003 GMC Sierra and Yukon with the same concern. Whether it is still current is not verified.

  • 3042Status unverified

    Service engine soon light or reduced engine power with P0120, P0220, P1516, P1518

    2003sierra-1500, yukon · issued · NHTSA 10009379

    Same GM concern as bulletin 3040 for the GMC Sierra and Yukon: reduced power mode or check engine light with the throttle and pedal codes set.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Nissan

  • 1995–1997 · Sentra

    Supported by vehicle data

    Nissan bulletin NTB98024A covers 1995 to 1997 models that show P0120 with the light on and no driveability complaint. Old and not verified as current.

  • NTB98024AStatus unverified

    MIL on with P0120, P0510, P0731, P0732 or P0733 and no driveability problem

    1995–1997altima, maxima, pathfinder, quest, sentra · issued · NHTSA 602818

    Nissan notes the light can come on with these codes while the car drives normally and points to a diagnostic procedure. Old bulletin; the summary gives no repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Cadillac

  • 2003 · CTS

    Supported by vehicle data

    GM bulletin 01108A covers an intermittent no-power or stall on the 2003 CTS with P0120 among many throttle codes. Not verified as current.

  • 01108AStatus unverified

    Intermittent no power or stall with throttle position and TAC codes

    2003cts · issued · NHTSA 10005466

    Covers an intermittent loss of power or stall with the check engine light and a long list of throttle-position and throttle actuator codes, including P0120.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0121The throttle position sensor A signal doesn't agree with what the engine computer expects, even though the voltage is within range

    Same system Supported by vehicle data

    P0121 is the range/performance version of the same throttle sensor circuit; GM lists them together in its 2003 bulletins.

  • P0122The throttle position sensor A signal voltage is below its normal range

    Same system Common general cause

    P0122 is the low-input form of the same circuit, so wiring checks apply to both.

All Electronic throttle and accelerator pedal codes

P0120 questions

Can I drive with P0120?

Only with care. If the car accelerates normally it may be an intermittent fault, but the computer can cut power without warning, so get it checked soon.

Is P0120 always the throttle position sensor?

No. Wiring, a loose connector or a dirty throttle body can set it, so check live data and the connector before buying a sensor.

Sources and review

  1. Chevrolet 3040: Service engine soon light or reduced engine power with P0120, P0220, P1516, P1518 — NHTSA manufacturer communications ,
  2. P0221 OBD-II code — Kelley Blue Book
  3. P0120 trouble code explanation — TroubleCodes.net
  4. P0120 OBD-II trouble code — PartsAvatar
  5. Cadillac 01108A: Intermittent no power or stall with throttle position and TAC codes — NHTSA manufacturer communications ,
  6. Gmc 3042: Service engine soon light or reduced engine power with P0120, P0220, P1516, P1518 — NHTSA manufacturer communications ,
  7. Nissan NTB98024A: MIL on with P0120, P0510, P0731, P0732 or P0733 and no driveability problem — NHTSA manufacturer communications ,
Last reviewed
Written by
Saurabh K.
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