Diagnostic guide for P2138

Diagnostic Guide for P2138 - Accelerator Pedal Position Sensor Correlation

The P2138 code indicates a discrepancy between the two Accelerator Pedal Position (APP) sensors in the vehicle. The goal of this diagnostic guide is to identify the root cause of the issue, which may involve inspecting the sensors, wiring, and the Engine Control Module (ECM).

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Difficulty

Intermediate

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Estimated Time

30-60 Minutes

Estimated Diagnostic Cost

$0-$100

Typical shop charge to perform this diagnostic process. Repair parts and labor are not included.

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Tools Needed

OBDII scanner, multimeter, wiring diagram, basic hand tools

Safety Notes

Ensure the vehicle is in park or neutral with the parking brake engaged. Be cautious of moving parts when the engine is running.

Step 1

Check for Existing Codes

Instruction Connect an OBDII scanner to the vehicle's diagnostic port and retrieve any stored trouble codes.

Expected result P2138 should be present along with any other related codes.

If Pass If P2138 is the only code, proceed to the next step.

If Fail If other codes are present, investigate those codes first as they may be related.

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Coddy can help with this step only. Tell me what you tested or what result you got.

Step 2

Inspect the APP Sensor Wiring

Instruction Visually inspect the wiring and connectors for the Accelerator Pedal Position sensors for any signs of damage, corrosion, or loose connections.

Expected result Wiring and connectors should be intact and secure.

If Pass If no issues are found, proceed to test the APP sensor signals.

If Fail Repair or replace any damaged wiring or connectors found during inspection.

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Step 3

Test APP Sensor Voltage Output

Instruction Using a multimeter, measure the voltage output of both APP sensors while slowly depressing the accelerator pedal.

Expected result Both sensors should output a voltage that increases smoothly from approximately 0V to around 5V as the pedal is depressed.

If Pass If both sensors output correct voltages, the sensors are likely functioning properly. Proceed to check the ECM.

If Fail If one or both sensors do not output the expected voltage, further investigate the faulty sensor or its circuit.

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Step 4

Check ECM Functionality

Instruction Verify that the Engine Control Module (ECM) is functioning correctly by checking for proper power and ground at the ECM connectors.

Expected result The ECM should have the correct voltage and ground connections.

If Pass If the ECM is functioning properly, consider the possibility of a faulty ECM or further issues with the APP sensors.

If Fail If power or ground is missing, trace the circuit back to find the fault.

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Step 5

Clear Codes and Test Drive

Instruction Clear the trouble codes using the OBDII scanner and perform a test drive to see if the P2138 code returns.

Expected result The vehicle should operate normally without the check engine light illuminating again.

If Pass If the code does not return, the issue may have been intermittent or resolved.

If Fail If the code reappears, further investigation into the APP sensors or ECM may be necessary.

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Coddy can help with this step only. Tell me what you tested or what result you got.