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Chevy Vehicles Have Wiring Glitch

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One area to inspect is under the driver’s sill plate as shown here. The red arrow indicates the front of the vehicle.

 

This bulletin applies to 2015-2019 Chevy Suburban, 2014-2019 Silverado, and 2015-2019 Tahoe vehicles. Some owners may comment on remote start inoperative, the power lift gate inoperative with ignition off, crank but no start or start and stall. 

On vehicles equipped with a diesel engine, the blower motor may stay on after the engine is turned off, which may cause the battery to drain. The SES MIL may be on, with codes P069E, P129D, P2537, U0137, U18A2, U0109, U012A, and/or U0100.

These concerns may be caused by the ECM and/or TCM or the FPDCM K111 not receiving the 12 volt accessory wake-up signal from the BCM. Reference the accessory wake-up circuit 5985 wiring diagrams in the service manual under Power and Signal Distribution/Data Communications/Schematic and Routing Diagrams/data Communication Schematic/Accessory Wakeup and Communications Enable. 

Using a voltmeter, check circuit 5985 at each of the modules. There should be approximately 12 volts present with the BCM awake. You may notice with the ignition turned off that there is still voltage present. This is because the BCM may still be awake. This should be considered normal. If no or low voltage is found, use the wiring diagram in the service manual and perform normal circuit diagnosis.

Circuit 5985 is a low amperage signal circuit and it may not be able to power certain test lights or bulbs. The use of a voltmeter and small bulb (example 194 bulb) is required to test the circuit. With a battery charger/maintainer connected, attach one side of a 194 bulb to circuit 5985 and the other side to a good ground (battery negative). 

Next, wake up the BCM (by turning on the headlights, ignition, etc.) and make sure that the bulb lights. If the bulb does not light, inspect for high resistance/open/shorts in circuit 5985. If the bulb lights, use a voltmeter and measure the voltage across the 194 bulb to make sure that there is at least 11 volts. If not, inspect for high resistance/open/shorts in circuit 5985.

Two known areas for high resistance/open/shorts in circuit 5985 are: for 1500 model trucks, inspect the chassis harness along the left frame rail in the area between the left rear body mount and the left front box/bed mount. For all models in general, inspect under the driver’s sill plate.

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