Transfer case mode has mind of it's own

TECHNICAL

Bulletin No.: 05-04-21-003C

Date: April 15, 2008

Subject:
Service 4WD Light Illuminated, DTC C0374 Set (Inspect Wiring Harness to Transfer Case Speed Sensors,, Replace Wiring Harness)

Models:
2004-2007 Buick Rainier
2003-2006 Chevrolet Avalanche, Suburban, Tahoe
2003-2007 Chevrolet Silverado Classic, TrailBlazer, TrailBlazer EXT
2003-2006 GMC Yukon, Yukon XL
2003-2007 GMC Envoy, Envoy XL, Sierra Classic
2003-2004 Oldsmobile Bravada
2005-2007 Saab 9-7X

With Four Wheel Drive or All-Wheel Drive

and Active All-Wheel Drive (RPO NP4) or Active Two-Speed (RPO NP8) Transfer Case

Supercede:

This bulletin is being revised to update the Model and Warranty Information. Please discard Corporate Bulletin Number 05-04-21-003B (Section 04 - Driveline/Axle).

Condition

Some customers may comment on intermittent illumination of the Service 4WD light. Upon investigation, the technician may find DTC C0374 set. The customer may also comment on intermittent erratic operation of the 4WD or AWD system after driving through rain/snow or simply going through a car wash.

Cause

The speed sensor signal may have become corrupted. Possible openings in the speed sensor wire insulation (twisted pairs) can allow water intrusion. Also wire connections contaminated by water may result in short circuits and erroneous speed sensor readings. This most often occurs on the rear speed sensor circuit.

Correction

Inspect the wiring harness to the transfer case speed sensors. On Rainier, TrailBlazer, Envoy and 9-7X models, fabricate a replacement speed sensor harness between the C101 connector and the speed sensors. Completely inspect and test all wiring. Refer to Speed Signal Front Axle Actuator and Indicators schematic in SI.

Replace the affected twisted pairs. Do not over-twist the two wires in the replacement harness. Wires should be twisted at a rate of 9 revolutions per foot. Use service connector pack, P/N 88987993 at the speed sensor end and terminal, P/N 15326267, at C101.

Terminal testing tools and service terminals can be found in Terminal Repair Kit J 38125. Terminals are available from SPX/Kent-Moore.

The smaller transfer case harness splices into the larger chassis harness a few inches in front of the crossmember. The chassis harness routes along the left side of the frame under the driver door area. Use nylon tie straps to secure the fabricated harness to the main chassis harness between the transfer case and C101.

On the full-size pickup and full-size utility models, replace the 2.2 m (88 in) pigtail harness that runs from the C151 connector under the hood to the transfer case. Use either harness P/N 15832722 or 15224663 depending on vehicle equipment. Refer to Propshaft Speed Sensors Front Axle Actuator and Transfer Case Shift Control Switch schematic in SI.

Important:
Technicians should verify the integrity of the splice joints after the repair. All splice joints and connections should seal properly against water or a repeat condition can occur.