here is a bulletin about water intrusion and this issue, I have seen several sunroof drains cause this but they say windshields and molding will too.
Subject:Intermittent Malfunction Indicator Lamp (MIL) Illuminated, DTC P2138 with Reduced Engine Power (Repair Instrument Panel (IP) to Body Harness Connector)
Models:2005-2015 GM Passenger Cars and Light Duty Trucks
Attention:For 2014 Model Year ATS, refer to the latest version of Product Emission Bulletin 14176 before proceeding with this Bulletin. This Bulletin also applies to any of the above models that may be Export vehicles.
This Bulletin has been revised to add Model Years, update the Labor Operations to the Global Labor Code (GLC) and to remove the Warranty Information (Saab U. S. Models) section. Please discard Corporate Bulletin Number 07-06-04-019D.
- Some customers may comment on an intermittent malfunction indicator lamp (MIL) being Illuminated with a message or an indicator that displays Reduced Engine Power.
- The technician may observe on a scan tool DTC P2138 – Accelerator Pedal Position (APP) Sensor 1-2 Correlation set as Current or in History.
This condition may be caused by water intrusion into the instrument panel (IP) to 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 P2138.
Note: Aftermarket equipment can generate DTC P2138 and/or other DTCs.
Note: Some examples of potential water leaks are: A-pillar seals, sunroof drain lines (if equipped) and windshield/cowl sealing.
- 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. Refer to Checking Aftermarket Accessories in SI.
- Perform the Diagnostic System Check - Vehicle.
- If any 5V reference DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
- If any 5V reference DTCs are not set, proceed to Step 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 SI.
- Inspect for a water leak in the area. If necessary use a water hose to determine the source of the leak. Refer to General Information > Water Leaks in SI.
- If a water leak is observed, repair as necessary. Verify the effectiveness of the repair.
- Inspect the IP to body harness connector terminals for corrosion and debris. Refer to Testing for Intermittent Conditions and Poor Connections in SI.
- If any corrosion and/or debris is observed, repair as necessary.
- After completing the repair, verify the proper operation of the system. Depending on the vehicle and model year, perform the Diagnostic Repair Verification procedure or refer to Diagnostic Trouble Code (DTC) List - Vehicle in SI.
For vehicles repaired under warranty, use the appropriate labor operation for the source of the water leak
Body Joint Resealing
Use Published Labor Operation Time
Plenum Panel Resealing
Note: Time for removal of necessary components to gain access to the leak and connector repair must be submitted as Other Labor Hours and have appropriate authorization.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
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