C0550 and no 4wd problems

[r-charger]

2004 envoy i6

My engine light is on. Code says C0550 ECU malfunction.
All the search results I get include the "TCCM is asleep", "no lights on the 4wd selector" and "4wd service light is on".

Not in my case. Just the engine light, Everything else works fine.

I tried pulling fuse 8 for 30 sec. no change.

Every time I erase it, it's pending again upon the next start up.

Any suggestions or ideas?

Thanks.

 

[IllogicTC]

If resetting by pulling the fuses did not help, it appears likely that you have a bad TCCM.

#02-04-21-006E: Inoperative 4WD/AWD Lamps, Inoperative 4WD/AWD System, DTC C0550 Set No Communication with TCCM (Reprogram Transfer Case Control Module) - (Jul 20, 2006)

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)

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.

 

[The_Roadie]

If your 4WD switch lights up and changes modes as commanded, you clearly don't have the dreaded "failure to wake up" problem. Perhaps just a broken data comm wire between the PCM and the TCCM. The TCCM is in standalone mode, doing its job. It just isn't telling the PCM it's alive. I'd be downloading the schematics and checking continuity on the data comm wire from the TCCM to the splice pack and then on to the PCM.

 

[r-charger]

Thanks guys, I'll dig out the multimeter....