2015 GMC Sierra P2138 Reduced Engine Power Mode

Question

My truck suddenly went into limp mode while cruising on the highway with the 'Reduced Engine Power' message on the DIC. I scanned it and found a P2138 code stored, and it feels like there is zero throttle response when I press the pedal. It clears and runs fine for about ten miles before the fault returns and kicks me back into limp mode.

Jordan Lee · Accepted Answer

The issue was a faulty Accelerator Pedal Position sensor assembly. I replaced the entire pedal unit with an OE AC Delco part (Part #23363065) which cost about $85. After swapping the pedal and performing a throttle relearn procedure with my scan tool, the correlation error disappeared and hasn't returned in over 2,000 miles. The sensor tracks inside the old unit had developed a dead spot.

hd_trucker_77 · Answer

Check the X151 connector located under the vehicle near the driver side body mount. Road salt and moisture often get into that harness and cause high resistance in the 5V reference circuits for the APP sensor.

Lina Brooks · Answer

Try spraying some electronics cleaner into the pedal assembly connector. Also, ensure your floor mats aren't catching the base of the pedal, as that can sometimes cause a mechanical discrepancy the sensor picks up.

Rachel Nguyen · Answer

You need to look at live data for APP Sensor 1 and APP Sensor 2. One should be exactly double the voltage of the other; if the ratio drifts by more than a few percent, the ECM triggers the P2138 immediately.

2015 GMC Sierra P2138 Reduced Engine Power Mode

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