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Dan
Dan, Auto Service Technician
Category: Car
Satisfied Customers: 3490
Experience:  GM ASEP A.A.S. 14 years GM experience. Mark of Excellence and Professional Guild awarded.
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Z71..4WD..my 2WD indicator light is now RED and I

Resolved Question:

2005 silverado Z71, I started the truck and the message center read "SERVICE 4WD" and the "AMBER" push button indicator lights didn't work. I shut truck off and re-started and everything was fine. The same thing happened the next time I started truck and the 3rd and each time after, no message appears but my 2WD indicator light is now "RED" and I can not change to 4H or 4L. Where do I start besides checking/changing fluids in the differentials and transfer and making sure the vacum lines are not disconnected or leaking?
Submitted: 6 years ago.
Category: Car
Expert:  Dan replied 6 years ago.
HiCustomer Thank you for asking your question on Just Answer. The other experts and I are working on your answer. By the way, it would help us to know:

-What year is your Car?
-What make and model is your Car?
-How many miles are on your Car?
-What type of engine is in your Car?
-What have you already tried?

Thank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.
Customer: replied 6 years ago.
Year: 2005
Make/Model: Chevrolet/Silverado Z71
Miles: 86,600
Engine 5.3 Liter
Already tried: Checked oil levels and Vacum lines.
Correction to fault: The 2WD "AMBER" light did not change from AMBER to RED, The Neutral light is RED, that is what was lit up. Yesterday at a traffic light it switched to 4L on it's own and the switched back to 2WD after about 200 feet. Now I have no indicator lights lit but the message center displays "SERVICE 4WD".
Expert:  Dan replied 6 years ago.

There severeal possibilities. Without actually scanning the 4WD system I wouldn't know for sure which bulletin applies. Here are some bulletins that do apply but would have to be performed by your dealer as it may require software upgrades, part replacement (with software upgrade) or at least scanning with the GM Tech 2 scan tool.


 

Subject:Intermittent Service 4WD Light Comes On With DTC C0306 Or C0308 Stored In TCCM - keywords 1625 1626 246 263 246EAU 263EAU 3023 case MIL NP1 NP8 NQF NQH transfer #PIP3526B - (12/08/2006)

 

Models:1999-2006 Cadillac Escalade
1998-2007 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe
1998-2007 GMC Sierra, Sierra Classic, Yukon, Yukon XL
Equipped with Transfer Case (RPO - NP8, NP1, NQH or NQF)

 


This PI is being superseded to add transfer case models. Please discard PIP3526A.


 

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

Service 4WD light comes on and the condition may be intermittent and hard to duplicate. DTC C0306 OR C0308 will be set in the transfer case control module.

Recommendation/Instructions:

If published diagnostics do not lead to a correction, check all grounds for poor connection. If the grounds shown in the transfer case schematics are clean and tight, also inspect the engine grounds, as other components grounding through suspect grounds can then seek other ground paths and interfere with transfer case operation. Battery cable engine grounds as well as grounds located on the back of the engine cylinder heads and engine block are possible sources of this concern.

Also make sure grounds are mounted to the correct location. For example, a ground that should be on the frame possibly moved to the core support during a previous repair may also cause this concern.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Subject:Electronic Transfer Case Unable To Complete Shift - keywords code DTCs hot inoperative #PIP3424A - (09/08/2006)

 

Models:1999-2000 Cadillac Escalade
2002-2007 Chevrolet Avalanche, Trailblazer
2004-2007 Chevrolet Colorado
1999-2005 Chevrolet Blazer, S10
1999-2007 Chevrolet Silverado, Suburban, Tahoe
2004-2007 GMC Canyon
1999-2007 GMC Envoy, Sierra, Yukon, Yukon Denali, Yukon XL,
1999-2005 GMC Jimmy, Sonoma
1999 GMC Suburban
2003-2007 Hummer H2
2006-2007 Hummer H3
with RPOs NR4, NP1, or NP8 Transfer Case

 


PI is being created to update models and years. Please discard PIP3424


 

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

 

Electronic transfer case may stop shifting if you repeatedly try to shift the transfer case in a short period of time and not set any dtcs

Recommendation/Instructions:

 

The software in the transfer case control module has a "shift abuse lock out" mode to protect the module and encoder motor. This concern will occur if the module senses repeated shift request in a short period of time. If the driver continuously tries to shift in and out of different modes, the transfer case control module will stop trying to shift for several seconds to prevent abuse damage to occur. Cycling the ignition off for 30 seconds or more should allow the transfer case to resume normal operation.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

 

Dan, Auto Service Technician
Category: Car
Satisfied Customers: 3490
Experience: GM ASEP A.A.S. 14 years GM experience. Mark of Excellence and Professional Guild awarded.
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