Engine Troubleshoot

P2138 Throttle/Pedal Position Sensor/Switch ‘D’/’E’ Voltage Correlation

What Does Engine Code P2138 mean?

  • P2138 Technical Definition: Throttle/Pedal Position Sensor/Switch 'D'/'E' Voltage Correlation
  • P2138 Meaning: Accelerator Pedal Position is not working as expected
  • Most common cause: Faulty Accelerator Pedal Position sensor or damaged wiring/connector
  • Risks for the engine/driver: HIGH Don't drive the car as it may be dangerous to do so
  • Emissions severity: LOW. The car should not have emissions problems
  • Estimated repair time: 1-2 days
  • Estimated repair cost: $200+

The OBD2 data trouble code P2138 is stored in memory when the Electronic Control Unit (ECU) detects a disparity between the signals from APP terminals D and E.

The Accelerator Pedal Position sensor (APP) is in charge of reporting the ECU the desired aperture of the throttle based on the driver’s pressure on the accelerator pedal.

The APP information is in turn used by the ECU to operate the Electronic Throttle Control (ETC) in real-time to follow APP ( the driver’s) decisions. Due to the huge importance of this sensor, it counts with an extra security measure called “redundancy design”.

What this means is that the APP consists of two internal sensors, the APP1 and APP2. Both sensors are identical but are installed with a predefined offset. The ECU is aware of that offset and uses it to compare the “expected value” from one sensor according to the information provided by the other. 

The P2138 code is set when the ECU detects a disparity often called “disagreement” between the returning signals from APP1 and APP2. Since APP information is used to control engine power this code should be considered as a potential threat to driver’s safety, immediate action is strongly recommended.


6 Common Symptoms When Code P2138 is Present

The most common symptoms of data trouble code P2138 are:

  1. Check Engine Light (CEL) lit.
  2. Throttle stuck open or closed.
  3. Lack of control over engine acceleration.
  4. Erratic acceleration control (lags).
  5. No acceleration.
  6. Idle speed higher or lower than normal.

Possible Causes For Error Code P2138

The most common causes of data trouble code P2138 are:

  • APP sensor wiring (open, shorted, burnt) 
  • APP sensor connector (loosely, corroded, disconnected or bent pins)
  • Bad APP sensor.

How To Diagnose The Engine Code P2138

For the purpose of this article, it’s assumed that you have a basic knowledge of safety precautions while working on your vehicle.

Always refer to the appropriate OEM literature when possible. Original manufacturer diagnostic procedures should always have precedence over a generic workflow.

That said, let’s start the diagnostic process!

1. Preliminary steps

To discard a possible intermittent DTC condition, you’ll need to clear the ECU memory and complete a driving cycle.

  • Read data trouble codes and take note of them.
  • Clear data trouble codes memory.
  • Perform a driving cycle (at least 5-10 minutes).

In case the Check Engine Light stays off then you may have an intermittent problem. If the light lit during your driving cycle then continue with the diagnostic process.

2. Visual Inspection

> APP sensor condition: to inspect the APP condition you will need to remove it from the vehicle. Usually, the Accelerator Pedal Position sensor is the same piece as the accelerator pedal. Check for any unusual condition like a broken sensor, broken wire, etc.

> APP sensor wiring and connector: perform a meticulous visual inspection of the Accelerator Pedal Position sensor wiring and connectors. Look for burnt, damaged, corroded or deteriorated wires, also unplug the sensor and look for bent terminal pins, loosely connections, corrosion or any other possible indication of a bad connection.

Fix any wiring problem before continuing.

3. Electrical Tests

> APP sensor electrical tests: using the appropriate OEM literature, check the sensor signal, and the reference voltage of the APP sensor. Reference voltage should be greater than 4.5V. Repair any circuit line as necessary.

4. Scan Tool Tests

> Accelerator Pedal Position sensor test: depending on your vehicle and automotive scanner, you should be able to put on screen the actual APP1 and APP2 signal values.

The values may be expressed on voltage, aperture percentage, or degrees.

Turn the key on, engine off (KOEO) and press the pedal to its wide open throttle position and then let it close again. Slowly depress the pedal and repeat again.

Watch the APP1 and APP2 readings. Graph the two values if possible. Both readings should be similar but with a small offset between them.

If you see a significative difference between the values or one of them does not change while pressing the pedal then you should replace the sensor. 


How To Repair Error Code P2138

Depending on the diagnostics results you may need to do the following:

  • Replace the Accelerator Pedal Position sensor.
  • Repair the Accelerator Pedal Position wiring or connector.