APPSensor

Accelerator Pedal Position Sensor (APP)

Group: Air and fuel

The APP sensor turns the position of the accelerator pedal into an electrical signal. On vehicles with an electronic throttle it replaces the cable: the computer reads the pedal and moves the throttle plate with a motor.

Contents

What does the APP sensor do?

For safety it has two independent tracks (APP1 and APP2). The computer compares both signals at all times: if they do not keep the expected relationship, it decides the pedal cannot be trusted, enters limp mode and limits acceleration. The same data is used for cruise control, traction control and the shift strategy.

Where is it located?

Built into the accelerator pedal assembly, under the dashboard. It usually has a 6-wire connector.

Signal type and reference values

  • Two 5 V supplies, two grounds and two signals.
  • Pedal at rest: track 1 around 0.5 to 1.0 V; track 2 around half of that, or running in the opposite direction, depending on the manufacturer.
  • Pedal to the floor: track 1 around 4.0 to 4.5 V.
  • Both tracks must move together and smoothly.

Values are a guide only: always check the manufacturer's data for your engine.

Symptoms of a bad APP sensor

  • The vehicle will not accelerate or responds with a delay.
  • Limp mode with the check engine light or the electronic power control light (wrench, EPC).
  • Normal idle but no response when you press the pedal.
  • Codes P2120 to P2138.

How to test the APP sensor step by step

  1. On the scan tool, watch the percentage of both tracks while you press the pedal slowly: they must rise together without jumps.
  2. Check the connector: the pedal sits in the footwell and sometimes gets wet or kicked.
  3. Check for 5 V and ground on both tracks.
  4. If one track has dropouts, the sensor is worn: usually the whole pedal is replaced.
  5. After replacing it, some vehicles need a simple relearn (ignition on, press and release the pedal several times following the manufacturer's procedure).

Trouble codes related to the APP sensor

Frequently asked questions about the APP sensor

What is code P2138?
It means the two tracks of the pedal sensor (or of the TPS, depending on the manufacturer) do not agree. The computer enters limp mode for safety.
Can the accelerator pedal be repaired?
Usually not: the sensor is built into the pedal and the whole assembly is replaced.

Updated September 25, 2026. Values are a guide only: always confirm them in the service manual for your engine.

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