I have a 2000 Chevy Blazer LT with auto 4wd. First, I know a lot has already been posted on 4x4 issues with Blazers which has been helpful, but I still have a question. While my mechanic was fixing another issue, he told me a "LOSS2COMM ATC Trans" code or something along those lines had been set. What is the actual code number so I can look it up more details? Is the ATC (automatic transfer case) different than the TCCM (transfer case control module)?

A brief history on my 4wd issues. I had the service 4wd light on about a year ago so I replaced the electronic dashboard switch buttons to no effect other than fixing the intermittent light. Then I looked at the TCCM itself after a dishonest mechanic took my money without finding a problem. Thanks to this website I found the issue because corrosion on some of the pins to the TCCM is a common issue. This eliminated the service light, and I though I was good. The 4wd does engage when I manually push the buttons, but I am not sure if the auto engage works. I have tried it in wet and snowy conditions and just can't tell. Do you think my "LOSS2COMM ATC Trans" code means the auto engage isn't working but the TCCM still is or is it just an old stored code (I have replaced the battery so I expected it would have cleared)?

Thanks for your help.

 

You are going to have to get the code from the mechanic. Every scan tool I have ever used has a different description for the code so there is no real precise way to determine the code that is stored from the description off the scan tool. It should be something VERY easy for the mechanic to provide.

 

I managed to get the code from my mechanic. It was a U1026 - LOSS CLASS2 COMM w/ ATC/TRANS. I looked at my TCCM connector again and one of the pins was pushed slightly back and corroded some more after I cleaned it last year. I cleaned it and pushed it back in. I think everything is running correctly.

It only seemed to be an issue at start-up because I can shift in 4wd by pushing the button. Isn't the code supposed to clear when it communicates with the module or does it always need an ignition cycle?

 

Do you have the 4-button or 3-button 4WD switch on the dash? The full diagnostic for the 3-button switch is in here (scroll down to the bottom; click on link). Even if you do have the 4-button, maybe some of the info might give you an idea how the TCCM "thinks" about things....

 

U1026 is a loss of communication with the TCCM. The code should clear, but it may take a few key cycles. If it keeps coming back, then you still have a problem with communication that is likely due to the corrosion at the connector to the TCCM.

Since there is an OBD2 trouble code concerning the TCCM, that means he has the NV236 4-button system. Plus he already stated he had "auto 4wd". You are proud of that page based on how many times you post the link, but the same information and more is detailed in the Tech Article (DIY) section here.