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Raindrops keep falling on my GM

Owners of 2005-2011 GM passenger cars and light trucks may comment about an intermittent MIL illuminated with a message or an indicator that displays reduced engine power. The technician may find DTC P2138 (accelerator pedal position APP sensor 1-2 connection set as current or in history).

This condition may be caused by water intrusion into the instrument panel (IP) to the body harness connector, which carries the APP sensor signals to the ECM/PCM. This water intrusion results in a voltage difference between APP sensor 1 and APP sensor 2 that exceeds a predetermined value for more than a calibrated period of time, setting code P2138.

NOTE: Aftermarket equipment can generate P2138 and other DTCs.

1. Verify that aftermarket equipment is not electrically connected to any of the APP sensor signal or low reference circuits or to any other ECM/PCM 5V reference or low reference circuits.

2. Perform a diagnostic system check. If any 5V reference DTCs are set, refer to the DTC list. If any 5V reference DTCs are not set, proceed to Step 3.

3. Locate the IP to body harness connector, which may be located in and around the left hand kick panel area or inside the IP. Depending on the vehicle and model year, refer to wiring systems or power and signal distribution in the service manual.

Examples of potential water leaks are A-pillar seals, sunroof drain lines and windshield sealing. Correct as needed. If any corrosion and/or debris is noted, repair as necessary.

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