My girl's 2002 TrailBlazer has a SERVICE 4WD light at the dash

[OR VietVet]

About a week ago, got up and TB would not crank and had a dead battery. Did locate the parasitic draw to a plugged in cell phone charger that the plug lights up when installed. Been a week since all this with no parasitic draw problems. I have a Power Probe PPDRAW tool that I use to monitor and found no further problems......EXCEPT....the SERVICE 4WD light is now on when started and stays on. Is causing no parasitic draw problems. I pulled codes and got U1026-Lost Class 2 Communications With ATC.....U1000-Class 2 Data Link Malfunction and C0550-ECU Malfunction.

There is no driving problems. The Drive selection switch does not light up. It is a 2wd-awd-4hi-4lo switch. I checked the ATC fuse by sight and both sides with test light. I also located the ATC module, d/s end of dash behind pop off panel. I unplugged all 3 connectors and plugged back in with no help.

The strange thing is that all was good till the dead battery and then this light comes/stays on now. I have also had key off and pulled the ATC fuse for 1 minute and reinstalled and no luck. My next step is to reattach my Foxwell NT710 GM only scanner and try to see where the communication problem lies.

 

[OR VietVet]

Codes found, U1026-Lost class 2 communications.
U1000-Class 2 data link malfunction.
C0550-ECU malfunction

 

[OR VietVet]

According to USPS tracking, I am supposed to get the incoming TCCM tomorrow afternoon. I will be either installing it tomorrow afternoon or likely Saturday afternoon-busy Saturday morning, or sometime Sunday. I will post the before and after pics here.

 

[George B]

I went through this with our 2002. It would fail when cold and work when warm. There is an issue with the early TCCMs in these where they don’t wake up after a power failure. I went through a couple dorman TCCMs with the same issue until I ordered one for a 2005 off ebay. That solved my issue. I may have posted about it on here somewhere.

Look around this search:

Google Search

 

[George B]

Codes found, U1026-Lost class 2 communications.
U1000-Class 2 data link malfunction.
C0550-ECU malfunction

Mine always has these stupid codes. Never fixed them and don’t care.

 

[OR VietVet]

I went through this with our 2002. It would fail when cold and work when warm. There is an issue with the early TCCMs in these where they don’t wake up after a power failure. I went through a couple dorman TCCMs with the same issue until I ordered one for a 2005 off ebay. That solved my issue. I may have posted about it on here somewhere.

Look around this search:

Google Search

Mine always has these stupid codes. Never fixed them and don’t care.

So, you had the codes with the TCCM from 2002. Replaced with a used 2005 and problem was solved and the same codes are still there? They won't clear? What problems were solved?

 

[George B]

So, you had the codes with the TCCM from 2002. Replaced with a used 2005 and problem was solved and the same codes are still there? They won't clear? What problems were solved?

The 2005 tccm solved the service four wheel drive issue and the four wheel has worked ever since.

 

[OR VietVet]

But still the same codes?

 

[George B]

But still the same codes?

I think the C0550 went away. That one is related to the TCCM but the U code has always been there when I scanned it.

 

[OR VietVet]

Yea, the C0550 is a powertrain code and the other 2 are instrument cluster and BCM.

 

[OR VietVet]

Ok, new TCCM is installed and all is working. Scrapes and some blood involved. SERVICE 4WD light now comes on to communicate and then goes out and the indicator lights up as should. Not too bad of an install. The hardest part was the module in the holding bracket and then reinstall the bracket, with 2 locator pins and 2 inch wide clip ears into the aluminum bracket mount. Gotta hold the tongue just right to line up and push in place. I now have the old TCCM and will contact the seller at ebay and see if he wants it. If not and someone here wants it, PM me and we will talk.

 

[OR VietVet]