Have a 4 WD question for our experts;thanks

[old Rusty C10]

Im moving this to 4WD for more responses for you

[Campbel45]

Jack it up so all four wheels are off the ground. Put it in 2wd, watch 2 wheels spin. Put it in 4wd and watch all 4 wheels spin. Easy as that. Take a video if you must to prove your vehicle is fine.


If something is wrong no fluid change is going to fix it. They are using that "fluid change" as an excuse to get you in the service door. If you dont have 4wd usually there is a solenoid or switch that has gone bad and it will throw a code. As a GM tech that is one thing Trail Blazers are good for...throwing codes.


Stay away from whoever you were talking to and best of luck on getting a new truck

[msgross]

Originally Posted by 77 ChevySport

OK; got my baseline. I was told to do this from another diss. board with some
very knowledgeable people: On drive pavement in 4WD "HI" take a turn under 5 MPH. If it feels like the brakes are being applied it is working. Guess what:
I tried this and it did feel like the brakes where being applied. Will talk to the dealer tomorrow. Larry

Which is what I said in post #5. I'm not very knowledgeable though. I've only owned 4WD's for 25 years, have 3 now and drove Hummer's for 20 years in the Army.

Originally Posted by old Rusty C10

Im moving this to 4WD for more responses for you

I think we've run this one into the ground, i'm unsubscribing.

OP, good luck with your purchase.

[77 ChevySport]

OK; problem solved; deal made. Thanks to all. Got good idea's from everybody. Solution was in the computer; got answer from retired Chevy/GM engineer. If anybodys cares here it is. Larry

The part number you should aim for is 12590220.

The dealer is a goof, and isn't reading their TSBs. 2002 TCCMs are HORRIBLY unreliable.


#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.

Important: For the 2002 model year, the TCCM must be replaced and reprogrammed.

Even if the encoder motor is bad on the transfer case, you can't tell until you get the TCCM communicating again and controlling the system. And if you need a new one, they're under $200 on Ebay. Just make sure you get the proper one (5-pin or 7-pin connector) and I forget which one the 2002 needs. I think the 5-pin. Until the vehicle has a working TCCM, no tech tool can POSSIBLY determine the encoder motor has an issue because the encoder motor can't be tested without the TCCM running well.

Unless the encoder motor has a big hammer hit in the side of it, and they blame THAT on the TCCM.