in our 03 D/A the service 4wd light is always on and the 4wd doesnt work. the 2hi 4hi etc. lights dont even light up. i tryed swapign the 4x4 push button switch with my dads 04 and no change, none of the lights light up. all fuses are good. dealer finds no codes.

I'm thinkin its the actuator in the Tcase but i dont want to spring for one so quick, anyone else experince this?

thanks guys

I would start with the switch myself, thengo after the actuator. Thses switches were noted for being problematic.

yea mine wont go in to 4lo and they said bring it in to change dash switch out first thing. so it must be a common problem

i took the switch out of my dad's 04 duramax and still no change, none of the lights light up and nothing changes.

also now the whole guage cluster has quite working, somtimes while driving it will cut out, no speedo, fuel, oil temp, tranny everything goes blank. it flickers randomly liek you start the truck and there is nothing and normally within a few seconds it cuts back in.

where do i start

Try this



2003 GMC Truck GMC K Sierra - 4WD (http://gsi.xw.gm.com/si/publications.do) | Sierra, Silverado (VIN C/K) Service Manual (http://gsi.xw.gm.com/si/showPubSection.do) | Driveline/Axle (http://gsi.xw.gm.com/si/showPubSubsection.do) | Document ID: 1848894
#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)


http://gsi.xw.gm.com/image_en_us/gif/000/999/999/999999995.gif 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).
<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1848894&from=sm#ss1-1848894">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.
<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1848894&from=sm#ss2-1848894">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®.
<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1848894&from=sm#ss3-1848894">Correction


<LI type=1>Try to communicate with the TCCM. If no communication, go to step 2. If communication is possible, go to step 5. <LI type=1>Remove the underhood (ATCM or TREC) TCCM fuse. <LI type=1>Wait 30 seconds. <LI type=1>Reinstall the fuse. The module should "wake up" and communicate with the Tech 2®. <LI type=1>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. <LI type=1>Reprogram the TCCM with the latest TIS software using normal SPS procedures.
Verify operation and that no codes are present.Important: For the 2002 model year, the TCCM must be replaced and reprogrammed.
<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1848894&from=sm#ss4-1848894">Warranty Information

For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
K4121
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.

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sniper7mm, you hit the nail on the head! i had checked all the fuses earlyer but there was no fuse in the TREC socket and i had no idea what it stood for. i threw a 30A fuse in TREC and boom 4wd works. thanks man!

and i also checked the dash fuses, guage cluster is still not working correctly, anyone else want to take a shot?:D