Chasing a 4WD problem

[TJBaker57]

That last screen shot doesn't show any TCCM related codes, just the EBCM and the general U1000.

The screenshot attached to post #33 shows 2 codes for the TCCM and 1 code for the PCM.

Nothing for the ABS/EBCM.

Based on the C0550 for the 4WD system it looks like the TCCM is toast.

 

[Mooseman]

All my searches say C0550 is for the EBCM. Even the new AI mech app says it's the EBCM. However, I did find THIS thread here that does say it's for the TCCM:

C0550 and no 4wd problems

2004 envoy i6 My engine light is on. Code says C0550 ECU malfunction. All the search results I get include the "TCCM is asleep", "no lights on the 4wd selector" and "4wd service light is on". Not in my case. Just the engine light, Everything else works fine. I tried pulling fuse 8 for 30...

gmtnation.com

And on the OS with the same TSB info:

fault code 550? what is it?

My friend has an 02 TB Ls with the service 4wd light on and the selector indicator light does not burn full time. It comes on all positions when you start the vehicle but then they go out. He had it checked at a local shop with a scanner. Not sure if it was obd2 or tech. but he said it had...

www.trailvoy.com

So I have egg on my face by proxy .

So the gist of the TSB says:

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.

So it does seem the TCCM may be toast. Picking one up at a pick-n-pull should be fairly cheap but try to get one from an 03+ as the 02 had defects.

 

[fechnerj]

Thanks for the followup. I ordered a used TCCM on ebay, will be delivered Monday. I'm not sure about year and I've read that sometimes a used one won't need refresh, but we'll see. I replaced one of these in my 03 and remember not a fun job, access bad, fingers have more arthritis

 

[flyboy2610]

I'm curious about your experience. Did you replace the actuator only or the complete disconnect/actuator assembly?

Only the actuator. I'd had to replace the disconnect assembly a couple of years earlier because a bearing self destructed. I didn't replace the actuator at that time.

 

[fechnerj]

Thanks for the followup. I ordered a used TCCM on ebay, will be delivered Monday. I'm not sure about year and I've read that sometimes a used one won't need refresh, but we'll see. I replaced one of these in my 03 and remember not a fun job, access bad, fingers have more arthritis

I looked at the ebay order again, and it's for 06-09, so should be good to go.

 

[TJBaker57]

looked at the ebay order again, and it's for 06-09, so should be good to go.

As far as I know they are all interchangeable.

I have like 7 different ones in my collection with 4 different calibrations and 5 different operating systems and they all seem to operate the same.

 

[fechnerj]

So, I installed the TCCM module purchased on ebay. Control of TC back to normal. No codes, no trouble codes, lights, etc.
Interesting that the original one installed in my 09 was date coded 2006. The used one is dated code 2009. Just interesting, don't know that it makes any difference, except it appears I don't have to get a dealer flash.

 

[TJBaker57]

appears I don't have to get a dealer flash

Only a brand new, never been used TCCM requires programming.

 

[MD_Envoy_Driver]

If you ever wondered in the middle of the night: "I wonder what my 4X4 center dash mode switch looks like on the inside?" Well, wonder no more........

 

[TJBaker57]

If you ever wondered in the middle of the night: "I wonder what my 4X4 center dash View attachment 119099View attachment 119100mode switch looks like on the inside?" Well, wonder no more........

BTDT

Also traced the circuitry and tested the various resistances and such.