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Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience:  Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
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2002 chevy trailblazer ls: 4wd..the transfer time..bucks

Customer Question

i have a 2002 chevy trailblazer ls 4wd, the indicator lights for the 4wd system do not come on , i have taken it in to find the problem before about a year ago and i was told that the transfer case did not get a "wake up " signale to wake up and had to be reset they said that next time this happens to read my manual to reset it my self , i cannot find the reset proceedure and i don't want to pay another 100 bucks if i can do it myself please help me thanks
Submitted: 9 years ago.
Category: Chevy
Expert:  Bob replied 9 years ago.

Hello, There is no actual reset procedure, I guess that is why you can't find it in the owners manual The actual reprograming on the unit is done with a class 2 scanner. The only thing you can try at home to reset the module is by removing the fuse under the hood. Look for a fuse labeled ATCM or TREC or TCCM. Once you have removed the fuse, wait 10 seconds and re install it. If this clears your condition, great. But, I have not seen it work very often. The correct way is to connect a class 2 scanner to the system and read any stored codes in the system and repair as needed. The codes will point you to the failed sensor or component. A regular code reader can't do this job as all they can read are codes related to the engine, emissions and transmission. This module is a class 2 electronic device so a class 2 scanner is the only thing that will interface with it. And the scanner is what is used to reprogram it. Below is another procedure that you may want to try and below that is what the factory says about it going to sleep. I hope some of this helps you. Thanks


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.


  1. Document ID#(NNN) NNN-NNNN
    2002 Chevrolet TrailBlazer - 4WD


    Subject:Inoperative 4WD/AWD Lamps, Inoperative 4WD/AWD System, DTC C0550 Set No Communication with TCCM (Reprogram Transfer Case Control Module) #02-04-21-006E - (07/20/2006)


    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).


    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.


    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®.


    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.

    Warranty Information

    For vehicles repaired under warranty, use:

    Labor Operation


    Labor Time


    Transfer Case Module - Reprogram with SPS

    0.4 hr


    GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

    © Copyright General Motors Corporation. All Rights Reserved.

    Document ID#(NNN) NNN-NNNN
    2002 Chevrolet TrailBlazer - 4WD