P2138 trouble code: What it means

Learn what a P2138 code means and how to fix the problem

Typical accelerator pedal position sensor (APP)

The P2138 trouble code is a diagnostic code that indicates an issue with the throttle/pedal position sensor/switch circuit. Specifically, it means a voltage correlation problem exists between the throttle position sensor (TPS) and the accelerator pedal position sensor (APP).

In modern vehicles, the throttle is controlled electronically rather than mechanically. When you press the accelerator pedal, sensors detect this movement and send signals to the engine control module (ECM). The ECM then adjusts the throttle accordingly. The P2138 code appears when there’s a discrepancy between what the throttle position sensor is reporting and what the accelerator pedal position sensor is reporting. In other words, a P2138 code means the two sensors in the accelerator pedal don’t correspond to one another.

How the sensors are wired

The ECM sends a 5-volt reference signal to both sensors and sees the return ground as a sign that the reference signal is reaching the sensors and returning back to the computer. A third wire carries that actual position signal. The voltage in one sensor is designed to rise as you accelerate, while the second sensor voltage reading should fall. They must both rise and fall at the same rate. If they don’t correlate, the ECM sets the code

How serious is this code?

This code is serious and must be fixed immediately. Keep in mind that this is a fly-by-wire vehicle, and the only way the system works is through electronic signals from the APP and TPS. If you don’t fix this immediately, you may encounter safety-related issues like:

• Potential safety hazards while driving
• Inconsistent acceleration
• Stalling
• Reduced fuel efficiency

How to diagnose a P2138 code

Check the APP connection— Disconnect the APP connector and check for corrosion or bent pins. Check the wiring harness for signs of chaffing or open wires.

Check for technical service bulletins— That carmaker may have issued a service bulletin on this problem, and that can save you a lot of time and expense

To test the APP, the vehicle must meet the following conditions:

• The system voltage must be greater than 5.23 volts
• The ignition switch is in the ACC, RUN, or CRANK position
• Trouble codes P0641, P0651, P2120, P2122, P2123, P2125, P2127, and P2128are NOT already stored in the computer

The computer looks at the difference between APP 1 and APP 2. If the two values exceed a predetermined value for more than .5-volts, it will set a P2138 code.

Press the accelerator pedal and watch the voltage change using the live data feature on the scan tool. The APP is bad if the voltage rise and fall values don’t match. Replace it

©, 2013 Rick Muscoplat