Service 4wd

[loganc]

Hey everyone,my 2003 GMC Sierra Z71 is not going into 4wd. I changed the transfer case motor encoder and still nothing. It has the push button with auto 4wd. The swithes are working. The code I got was C0321- Transfer case circuit lock malfunction. When the weather got warmer the service 4wd drive was gone. When I pushed the button to engage it flashed for about 10 seconds and the service 4wd came back on. Any help would be great

[Matt_]

there's a TSB out there for the 2003 model year trucks... i believe programming error would cause this problem and the fix was just a quick reflash at the dealer.

 

i'll post up the TSB number if i can find it. It might be # 030421001...

 

Edit: Nevermind... you don't have the right DTC

 

Bulletin No.: 02-04-21-006E

 

Date: July 20, 2006

 

TECHNICAL

Subject:

Inoperative 4WD/AWD Lamps, Inoperative 4WD/AWD System, DTC C0550 Set, No Communication with TCCM (Reprogram Transfer Case Control Module)

 

Models:

2004 Buick Rainier

2002-2004 Chevrolet TrailBlazer, TrailBlazer EXT

2003-2004 Chevrolet Avalanche, Silverado, Suburban, Tahoe

2002-2004 GMC Envoy, Envoy XL

2003-2004 GMC Sierra, Yukon, Yukon XL

2004 GMC Envoy XUV

2002-2004 Oldsmobile Bravada

 

with Electronic Shift or Active Transfer Case (RPOs NP1, NP4 or NP8)

 

Supercede:

 

This bulletin is being revised to add Subject information and change the labor operation. This bulletin cancels and supersedes Bulletin Number 03-04-21-006. Please discard Corporate Bulletin Numbers 02-04-21-006D and 03-04-21-006 (Section 04 - Driveline/Axle).

 

Condition

 

Some customers may comment that the 4WD/AWD indicator lights on the selector switch do not work, or the 4WD/AWD system may be inoperative and/or the service 4WD light is illuminated. The condition is typically intermittent and always occurs at key-up. Upon investigation, the technician may find DTC C0550 set.

 

Cause

 

The Transfer Case Control Module (TCCM) has not received the wake-up call during key-up and has remained in the "sleep mode".

 

When the TCCM is in the "sleep mode", it will not communicate with the class II bus or the Tech 2®.

 

Correction

1. Try to communicate with the TCCM. If no communication, go to step 2. If communication is possible, go to step 5.

 

2. Remove the underhood (ATCM or TREC) TCCM fuse.

 

3. Wait 30 seconds.

 

4. Reinstall the fuse. The module should wake up and communicate with the Tech 2®.

 

5. Check for codes in the TCCM. If a C0550 is found current or in history with or without other codes, replace the module and go to step 6.

 

6. Reprogram the TCCM with the latest TIS software using normal SPS procedures.

 

7. Verify operation and that no codes are present.