15 codes after transfer case fluid change

[jhenry999]

Have '03 Trailblazer w/selector switch 4WD. Never use 4WD. Changed transfer case fluid at 164,000 miles. Used AutoTrac II (blue stuff). Earlier changes' mileage unknown. Service Engine light came on after 200 miles. Had 15 codes: such as CO359 , CO374, etc...all transfer case related with "No Code Definition" available for any one of those with O'Reilly code reader. Had one PO128, "Coolant Thermostat" code. Any ideas short of the $100 dealer diagnostics?

 

[gmcman]

After you changed your fluid, did you test the 4WD in any way? Either just turn it on or try to drive? If so, then perhaps the encoder motors may have not either engaged or fully engaged.

Going from 2WD to A4WD, you should hear one motor engage, do you? Then continuing to 4HI, do you hear another?

Do this with engine off, key on.

Can you list all the codes?

 

[dfc739]

First I would check the fuses. Then I would crawl back under there and check to make sure you didn't bump any electrical connectors or if any accidentally came unplugged. Also check your grounds to make sure none are loose/corroded.

If those don't correct the problem: what else can you tell us about how it acts? Is it 100% business as usual- no unusual lights aside from the CEL? Does it drive normally? Is 4HI an option and have you tried it?

 

[jhenry999]

One more thing: I replaced the battery. Saw an old post about multiple codes after a battery replacement and now wonder if the computer is reading historical codes. Here's what I got: PO128 (that's easy: coolant thermostat issue), but then all of this: CO327,CO321,CO306,CO305,CO300,CO237,CO359,CO374,CO379,CO550,BO775,BO780,BO785,BO790,B2725,CO235...with the message " No Code Definitions Available" on the printout from O'Reilly's Auto Parts store, but with all Transfer case-related reported fixes. I Never use the 4WD. Kind of afraid to put it in 4WD now...it might get stuck if actuator motor is not working. How do I REALLY clear the computer? I've got the battery disconnected at the moment. Thanks.

 

[Mooseman]

You can Google all codes and should give you the definitions. You can probably drive it like this as most likely it's the transfer case and will just stay in 2wd until fixed. You can buy a Bluetooth ELM OBD interface and Car Gauge Pro for Android to read and clear all codes.

That thermostat code you should fix ASAP before you damage the CAT.

 

[Mounce]

Also since you're resetting the pcm by having the battery disconnected you're gonna want to clean the throttle body. If it's dirty and the pcm get reset without the TB getting cleaned you will likely experience random stalling that won't go away for many miles.

 

[djthumper]

To begin with those Os should be 0s (zero). They are related to the TCCM area and the front axle. There is an old TSB out there on bad communications to the TCCM, which is what it sounds like is happening to you. I would definitely check the grounds and see if you accidentally pulled a wire.

Bulletin No.: 02-04-21-006E

Date: July 20, 2006

TECHNICAL
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)

Supercede:

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.