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P2128 OBD-II Trouble Code: Throttle/Pedal Position Sensor/Switch "E" Circuit High Input

Check Engine Light

P2128 trouble code definition

The pedal position sensor is used as an input to the engine control module (ECM) to determine the amount of torque requested by the operator. The ECM should receive an input that is within the specifications set by the manufacture. If not, a code P2128 may be set.

What the P2128 code means

The pedal position sensor is a hall effect style of sensor and it should change its voltage according to the angle of the gas pedal assembly. The engine control module will supply the pedal position sensor with what is known as a reference voltage.

Your specific make or model of vehicle will determine whether the voltage increases or decreases as the pedal is depressed. Usually, as the gas pedal is pressed, the pedal position sensor will decrease its produced voltage. There is a specific resistance that should be applied by the pedal position sensor as the accelerator pedal is at rest and when it is depressed.

Resistance acts as a sponge for voltage and absorbs volts as they pass through the circuit. The voltage will exit out of the pedal position sensor and will be sent back to the ECM. The ECM will use this data for engine management such as adjusting the air-fuel ratio and ignition timing. If the ECM determines that the voltage it is receiving is too high, a code P2128 will be set.

What causes the P2128 code?

  • A faulty pedal position sensor
  • Poor electrical connection of the pedal position sensor
  • Open or short circuit condition of wiring associated with the pedal position sensor
  • Faulty ECM

What are the symptoms of the P2128 code?

  • Engine hesitation
  • Check Engine Light illumination
  • Engine lack of acceleration

How does a mechanic diagnose the P2128 code?

  • Inspecting the circuit of the pedal position sensor for poor connections, corrosion, fraying, opens, or shorts

  • Using a scan tool to view the live data of the pedal position sensor while operating the pedal

Common mistakes when diagnosing the P2128 code

There are usually two pedal position sensors used on post-2013 vehicles. It is important to distinguish the two with an appropriate diagram when diagnosing this trouble code. Some mechanics have replaced the wrong sensor unknowingly.

How serious is the P2128 code?

This code is quite serious because the pedal position sensor tells the ECM how much torque the operator is requesting. If it is faulty, in theory and from experience, the sensor may tell the ECM it is at full throttle while only one fourth of the way depressed, which is very dangerous.

What repairs can fix the P2128 code?

  • Repair or replacement of any damaged wiring or electrical connections associated with the pedal position sensor

  • Re-flashing or updating the ECM

  • Replacing the pedal position sensor

Additional comments for consideration regarding the P2128 code

On many late model GM vehicles, there will be an ECM update related to the pedal position sensor. Many mechanics have replaced the pedal position sensor in belief that it will solve the trouble code P2128, while all along it needed an ECM update and not a replacement of the sensor.

Need help with a P2128 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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