P2128 Accelerator pedal or throttle sensor E signal reading too high

Throttle/pedal position sensor/switch E circuit high

P2128 in short

P2128 means the computer sees a throttle or accelerator pedal position sensor (circuit E) reading higher than expected. The usual causes are a pedal sensor, a bad connection, damaged wiring or, less often, the computer. The car may run with reduced power. Get it diagnosed soon and stop if power drops suddenly.

Electronic throttle systems use several position sensors so the computer can cross-check them. Circuit E is one of these signals, on the pedal or the throttle depending on the car. P2128 sets when that signal sits above the allowed range.

PartsAvatar lists a faulty pedal position sensor, a bad connection, a disconnected or shorted wire and the engine computer. GM bulletins list P2128 among several pedal and throttle sensor codes that come with intermittent check engine lights and reduced engine power on Trailblazer, Tahoe and Suburban models.

Which part carries sensor E differs by vehicle, so read the service information for yours before replacing the pedal or the throttle body.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Accelerator pedal position sensor or assembly

    Common general cause
    Why it ranks here
    PartsAvatar puts the pedal sensor first, and GM groups P2128 with pedal sensor codes.
    What would change this
    Rises if the sensor E voltage is stuck high on a scan tool or does not follow the pedal. Falls if the voltage follows the pedal smoothly.
    How to test the accelerator pedal position sensor

  2. Bad connection or damaged sensor wiring

    Common general cause
    Why it ranks here
    PartsAvatar lists a bad connection and open or shorted wiring. A short to power gives a high reading.
    What would change this
    Rises if the reading jumps when the harness is moved. Falls if a connector and harness test good.

  3. Throttle body position sensor (where E is on the throttle)

    Possible — needs testing
    Why it ranks here
    On some designs sensor E is in the throttle body, so a failed throttle sensor or motor can set it.
    What would change this
    Rises if the service information puts sensor E on the throttle and wiring tests good.
    How to test the electronic throttle body

  4. Engine computer fault or needed update

    Possible — needs testing
    Why it ranks here
    PartsAvatar lists the computer and an ECM reprogram as fixes, but this ranks last until the sensor circuit tests good.
    What would change this
    Rises only after the sensor and wiring pass.
    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 codes and watch the throttle and pedal position values with the key on and engine off, then press the pedal slowly.

    Low riskTool: OBD-II scan tool

    • IfSensor E is stuck high or does not follow the pedal

      It meansCheck the sensor and its connector.

      Go to step 2

    • IfOther pedal or throttle codes are stored

      It meansDiagnose the throttle system together, starting with the shared wiring.

      Go to step 2

    • IfValues follow the pedal smoothly and the code is not active

      It meansIntermittent; check connectors and harness.

      Go to step 2

  2. Inspect the pedal and throttle connectors and harness for corrosion, loose pins and chafing, and wiggle the harness while watching sensor E.

    Use cautionTool: scan tool, flashlight

    Warning:Keep fingers out of the throttle opening with the ignition on. The motor can snap the plate shut.

  3. Back-probe the sensor connector and compare reference voltage, signal and ground with the service manual.

    Best left to a shopTool: multimeter, service manual

    Warning:Never short the sensor reference pin to ground, which can damage the computer.

Symptoms

  • Engine slow to respond or reluctant when you press the pedal
  • Poor acceleration or reduced power
  • Check engine light, sometimes with other throttle warnings
  • Power drops sharply or the engine stalls Gets more serious: stop and have it checked.

Compare with: Check engine light with loss of power

How to fix

  1. Ask a dealer whether your VIN has an open software update or bulletin for pedal or throttle sensor codes.

Parts and cost context

  • Accelerator pedal position sensor:On many cars the sensor is part of the pedal assembly, so the whole assembly is replaced. Confirm the cause first, and ask for 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

  • 2007 · Tahoe

    Supported by vehicle data

    GM bulletin 08-06-04-012 lists P2128 among pedal and throttle sensor codes with an intermittent check engine light and reduced power. Whether it is still current is not verified.

  • 2004 · Trailblazer

    Supported by vehicle data

    GM bulletin 01746 covers pedal or throttle sensor codes including P2128 on 4.2L and 5.3L engines. Whether it is still current is not verified.

  • 08-06-04-012Status unverified

    Intermittent MIL/SES with pedal and throttle sensor DTCs including P2128

    2007suburban-1500, tahoe · NHTSA 10024742

    Intermittent check engine light with reduced engine power and several pedal and throttle sensor codes including P2128. The NHTSA summary does not give the repair. Also covers GMC and Cadillac models.

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

  • 01746Status unverified

    4.2L/5.3L engines with DTC P2120, P2122, P2123, P2127 or P2128

    2004trailblazer · NHTSA 10006289

    Pedal or throttle position sensor codes including P2128 on 4.2L and 5.3L engines. The NHTSA summary does not give the repair. Also covers GMC Envoy, Buick Rainier and Oldsmobile Bravada.

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

Ford

  • 2015–2017 · F-150

    Supported by vehicle data

    Ford bulletin SSM 46829 covers this code: intermittent loss of throttle pedal response, F-150. Whether it is still current is not verified.

  • SSM 46829Status unverified

    Intermittent loss of throttle pedal response, F-150

    2015–2017f-150 · NHTSA 10119677

    Intermittent loss of throttle pedal response with a wrench light and other warnings on some F-150s; the bulletin lists P2128 among the pedal sensor codes.

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

  • P2127The signal from the second accelerator pedal position sensor (sensor E) is below its normal range

    Other bank Possible — needs testing

    P2127 is the matching low-signal code for sensor E; read them together to tell a short to power from an open or short to ground.

  • P2138Two accelerator pedal position sensor signals (D and E) that should agree with each other don't

    Shares causes Supported by vehicle data

    GM groups P2128 with P2138 (pedal sensor D/E correlation) in the same reduced-power bulletin; diagnose both together.

All Electronic throttle and accelerator pedal codes

P2128 questions

Is the pedal or the throttle body at fault with P2128?

It depends on the car. Sensor E sits in the pedal on some designs and in the throttle body on others, so check the service information and test the circuit first.

Sources and review

  1. OBD Code P2128 - Throttle Position Sensor/Switch E Circuit High Input — PartsAvatar
  2. GM 08-06-04-012, intermittent MIL with throttle and pedal codes including P2128 — General Motors via NHTSA
  3. GM 01746, engine with DTC P2120, P2122, P2123, P2127 or P2128 — General Motors via NHTSA
  4. Ford SSM 46829, Intermittent loss of throttle pedal response, F-150 — Ford via NHTSA
Last reviewed
Written by
Saurabh K.
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