Alaskans 4x4 not working x2 ????

[bigdan]

Hello all. Greetings from Ak. We had a '02 Envoy in the shop the other day with a no 4x4 complaint. We could not get the transfercase computer to interface with our scanner. (Top of the line Snap-On) All the fuses were good. The lights on the switch would not work, and there was no transfercase action. We fought with it for the better part of a day and then punted.

This week we have a '02 Trailblazer in the shop with guess what? No 4 wheel drive. This time the t-case computer will interface with the scanner, but will not respond to prompts. Ie, flash the switch lights, engage, dis-engage, etc. Have any of you guys had similiar problems where your 4x4 just totally went out? Any help would be greatly appreciated.

[2002BlkLTZ]

Had a simliar problem. Couldn't get the TCCM to interface with similar snap-on scanner. Ended up needing a TCCM, $400 and some change from the stealership. Good luck. Possibly can get by with a reflash of the current module, but from what I've seen they're usually replaced. Curiously enough my stealership had TCCM's in stock, which I thought indicated their propensity to fail.

[bmm354]

From this example and other posts I've seen this does seem to be a common problem. There is at least one service bulletin out there that calls for the t-case module to be reprogrammed in this instance for 2002-03 TBs, Envoys, and Bravadas. But as 2002BlkLTZ mentioned I have a feeling in many cases a module replacement will be the only fix.

However, try this before doing anything further if the indicator lights on the 4x4 selector switch don't light, the 4x4 system is dead, and/or the Service 4WD light is on:

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

Correction
-Remove the underhood (ATCM or TREC) TCCM fuse.
-Wait 30 seconds.
-Reinstall the fuse. The module should "wake up" and communicate with the Tech 2®.
-Check for codes in the TCCM. If a C0550 is found, replace the module and go to the next step. If other codes are found, they may be related to this concern, go to next step and recheck for codes.

-Reprogram the TCCM
-Verify operation and that no codes are present.

Good luck!

[bigdan]

Thanks for the info guys.

We have communication through the scanner now. New switch installed. Guess we'll send it to the stealer for a re-flash. hmmm...