Author Topic: 2005 Chevy Silverado "Service 4wd" Light  (Read 14636 times)

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2005 Chevy Silverado "Service 4wd" Light
« on: December 03, 2009, 03:57:27 PM »
At about 60K miles, the Service 4WD light would come on intermittently.  Sometimes the 4WL light would be on, sometimes the red light, and occasionally no lights would be illuminated at all on the Transfer Case Shift Control Module mounted on the dash.  I replaced the switch module and the problem went away for a while.  The problem has now resurfaced at 90K miles and started out just like before.  It then started occasionally shifting into 4WD at engine start.  Now, the Service 4WD light comes on immediately when the key is turned on.  All of the lights on the module come on and then go off which is normal I believe.  I removed the module and put it in my wife's 2001 Tahoe and it worked just fine.  There are no ODB codes being generated.  I disconnected the battery (suggested in another forum) with no change.  I have regularly exercised the 4WD by driving in each of the ranges.  I'm at a loss.  Any help would be greatly appreciated!

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  • Guest
Re: 2005 Chevy Silverado "Service 4wd" Light
« Reply #1 on: December 07, 2009, 11:19:08 PM »
They have had lots of issues with the 4x4 switches on those, also a few issues with the encoder motor on the t-case itself. As far as codes go, a generic scanner likely will not pull transfer case codes, if the service 4x4 light is on, it knows something is wrong therefore tossing a code along with the light. If you have a vehicle to swap parts with, try swapping the encoder motor, the black L shaped piece right behind the front output yoke on t-case. Dont expect success, just a suggestion and i cannot say for sure that they are identical 01-05, if you have a friendly gm parts guy, might be worth the call, also a junkyard likely knows all the interchangeables. But if it is stuck in 4 wheel, the encoder is LIKELY suspect. The ideal way to go is pull the codes with a capable scanner and check back with us with more info before turning any wrenches, -Why work harder if you can work smarter

*One more thing, DO NOT turn the encoder motor by hand off the truck, if the one is stuck in 4 wheel, make sure the donor part is in 4 wheel upon removal. I believe there is a big yellow dummy sticker on it for that reason.

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Re: 2005 Chevy Silverado "Service 4wd" Light
« Reply #2 on: December 08, 2009, 05:42:46 AM »
Address TSB # 05-04-21-003.

Subject: Service 4WD Light Illuminated, DTC C0374 Set (Inspect Wiring Harness to Transfer Case Speed Sensors, Replace Wiring Harness) #05-04-21-003A - (03/03/2006)

Models: 2004-2006 Buick Rainier

2003-2006 Cadillac Escalade Models

2003-2006 Chevrolet Avalanche, Silverado, Suburban, Tahoe, TrailBlazer, TrailBlazer EXT

2003-2006 GMC Envoy, Envoy XL, Sierra, Yukon, Yukon XL

2003-2004 Oldsmobile Bravada

2005-2006 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


This bulletin is being revised to add the 2006 model year, Saab 9-7X model and clarify model usage information in the Correction section. Please discard Corporate Bulletin Number 05-04-21-003 (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. 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. Use service connector pack, P/N 88987183, 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. Call 1-800-GM-TOOLS (1-800-468-6657).

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 15224661 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.

Parts Information
Part Number
Description

15224661
Harness Asm-Transfer Case Sel

(4WD Full-Size Pickup/Utility w/NP8 and without Four Wheel Steering (NYS)

15224663
Harness Asm-Transfer Case Sel

(4WD Full-Size Pickup/Utility w/NP8 and Four Wheel Steering (NYS)

88987183
Connector-w/leads, 2-way, Female (Speed Sensor)

(All Vehicles)


Warranty Information (excluding Saab U.S. Models)
For vehicles repaired under warranty, use:

Labor Operation
Description
Labor Time

N6630
Wiring And/Or Connector-Transmission/Transfer Case/Transaxle/Front and Rear Axle Control - Repair or Replace
Use published labor operation time


Warranty Information (Saab U.S. Models)
For vehicles repaired under warranty, use:

Labor Operation
Description
Failed Object
Fault/Reason
Location Code
Warranty Type
Repair/Action Code
Labor Time

3714901
Wiring And/Or Connector-Transmission/Transfer Case/Transaxle/Front and Rear Axle Control - Repair or Replace
37149
67
0
01
01
Use Published Labor Operation Time

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