My wife's 98 Blazer is having some issues. The lights on the 4WD dash switch will go out. When this happens the Blazer may or may not put itself into 4WD. Pushing the 2Hi button will sometimes get it to switch back, but sometimes it takes a few minutes of playing with it. I have replaced the switch, it didn't help. I also pulled the fuse and cleaned it a little. When I put it back in, everything seemed to work as it should. By the next day, the problem was back. I'm thinking now it's something in the computer. Anyone have any experience with this problem? Can I temporarily disconnect and plug the vacuum line to keep it in 2wd until I find the problem? Thanks for your help.

 

This could be caused by corrosion on the TCCM located behind the passenger side kick panel (in front of the passenger door). Pull the kick panel and then check the connections to the TCCM.

 

I checked the connection. It did not look bad, but I still tried to clean everything a little. When I put it back together, everything seemed to work right. I went out and started it up a few hours later, and no lights on the switch, buttons didn't do anything. Is it likely the TCCM is bad? Is there a way to test it before I spend money to replace it? Thanks.

 

This is where I am now. I can switch to 4 hi, but then the lights usually go out, and I can't get back to 2 hi. If the lights stay on, it switches back and forth like it should. TCCM is not storing any codes. If I pull the fuse for a while, it should at least give me a DTC 1, right? I swapped the TCCM with a used one from a salvage yard. Should I exchange it for a different one, or is the problem likely somewhere else? Thanks for your help.

 

Have you checked the connections at the encoder motor as well as the switch itself?

Also, do you have the 3-button (NV233) or the 4-button (NV236) switch on the dash?

 

It is the 3 button switch. The first thing I did was replace the switch with a new one. I will check the other connections. If I pull the fuse or unplug the TCCM, shouldn't I get error code 1 when I re-connect it? It is not storing any codes.

 

I have had some give me code 1 after a battery disconnect and then others not, all of which were properly functioning. IMO, it should give you that code, but what it should do and what happens in reality aren't always the same.

If you really want to dig into the diagnosis, check out the thread by error_401 in the Tech Article (DIY) section about the NV233.