Rick's Free Auto Repair Advice

Service 4WD Light on

How to fix a Service 4WD Light on, C0374 on GM vehicles

GM has issued a technical service bulletin (TSB) 05-04-21-003B to address a Service 4WD light on, C0374 on GM models:

2004-2007 Buick Rainier
2003-2007 Chevrolet Avalanche, Silverado Classic, Suburban, Tahoe, TrailBlazer, TrailBlazer EXT
2003-2007 GMC Envoy, Envoy XL, Sierra Classic, Yukon, Yukon XL
2003-2004 Oldsmobile Bravada
2005-2007 Saab 9-7X

In addition to a lit Service 4WD light, you may notice erratic operation of the 4WD or AWD, especially after driving in rain, snow, or after going through a car wash. GM has determined that the speed sensor may be providing corrupted information due to water intrusion through the wires. In addition, the water may short and provide incorrect speed sensor readings. This usually occurs on the rear speed sensor.

GM advises checking the wiring to the transfer case speed sensors. On Rainier, TrailBlazer, Envoy and 9-7X models, you must fabricate a replacement speed sensor harness between the C101 connector and the speed sensors. Since this is a data connection, you must twist the wires at the rate of 9 twists per foot.

On the full-size pickup and full-size utility models, GM recommends that you replace the pigtail harness that runs from the C151 connector under the hood to the transfer case.

GM has issued part numbers for replacement terminals
Part Number Description
15832722 Harness Asm-Transfer Case Sel for (4WD Full-Size Pickup/Utility w/NP8 and without Four Wheel Steering (NYS)

15224663 Harness Asm-Transfer Case Sel for (4WD Full-Size Pickup/Utility w/NP8 and Four Wheel Steering (NYS)

88987993 Connector-w/leads, 2-way, Female (Speed Sensor) for (All Vehicles)

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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