I have a strange issue that is occurring with my 4x4 blazer. It seems that (even after transfer case control module was replaced), every week or two my blazer refuses to engage the 4 wheel drive. Buttons do nothing, except for 4x4 low when in neutral, which switches normally, then back to 2 wheel when in neutral. If I unplug the battery for a few hours to reset everything then the 4 wheel drive works flawlessly for another week or two. After that, the same problem happens again. Does anyone have any idea what the cause of the problem could be? Since it’s 23 years old no dealer knows how to work on it and any parts for the 4 wheel drive are out of production and can’t be found. I’m hoping this forum would be able to give me some ideas as to what to look at.

Thanks.

 

Hi,

This is the place to ask these questions.

A not so uncommon issue can be with the transfer case control module (TCCM) located behind the passenger side kick panel. When these start to fail, you will be able to hear several clicking noises from the TCCM. These are the PCB mounted relays. They should only click once. But there is an issue with the board, then they may click several times before the system engages (or not). There have been reports that the electrical connection to these can become corroded causing similar issues and symptoms.

Do any of these apply to you?

 

The TCCM was replaced in 2024. And when I am able to engage or disengage the 4 wheel drive it does only click once. When the problem occurs there is no clicking of the TCCM, the 4Hi, and 2Hi buttons do nothing in any gear including park. In neutral, I can push the button for 4Lo and that does click and I can hear the “thunk” from the transmission when it kicks in. I can also switch back to 2Hi with no problem in neutral only. In any other gear the buttons make no indication that they were even pressed. If I unplug the battery for a few hours, everything returns to operating normally. I can shift from 2Hi to 4Hi in any gear. But this only works for a couple weeks, then back to no button response, and I have to repeat the battery disconnection in order for the buttons to respond again.

I don’t think this has to do with the button module since they obviously work after the power disconnection.

 

Dang. Yes, I agree that this is not related to the TCCM. I had wondered if it was a battery issue with it being lower due to cold weather, but that would not be an issue since you would only change the drive configuration when the engine is running.

Do you have the 3-button or 4-button transfer case? With that information I can look in my service manual to see if it has any suggestions.

Perhaps someone else has some ideas too.

 

It’s a 3 button transfer case. I’d love any suggestions anyone can provide. This was happening during the summer months as well, so I don’t think it’s a temperature issue. And just to cover the power issue, I just had the battery replaced last month. And, yes, I only change while the engine is running, and usually in drive.

I’d definitely appreciate any help either you or others on the forum could provide! Just for further information, the Blazer is an LS 4 door, 4.3L engine.

 

thanks for the info on tccm and the clicking, i would probably pull the 10 amp fuse located in the side dash instead of disconnecting battery

 

I actually did try pulling the fuse from the inside and under the hood for a few hours. That did not help. Only disconnecting the battery proved to solve the issue temporarily.

 

Take a look for the ATC fuse in the underhood fuse box (which is hot at all times) to cut power to the TCCM and reset it instead of pulling the battery. See how that works out for your reset needs.

*EDIT* -- Looking at the schematic, I also see that the TCCM gets a *hot at all times* power through the CTSY LP fuse in the instrument panel fuse box so perhaps both fuses would need to be pulled at the same time...? Maybe pulling the battery is easier? Seems silly to power a device off of a completely unrelated circuit...

As far as the problem is concerned, it is likely that there is something going on with the encoder motor that the TCCM is finding fault with and the reset brings it back around until it sees the issue again.

 

I did the reset again today, only for an hour this time because of extremely cold weather this evening. The button for 4Hi came on and I attempted to take it for a spin, however this time the front wheels did NOT engage as they have done previously and went back to buttons not responding almost immediately after the first press. My previous battery disconnections have been for longer than an hour, so maybe that had something to do with everything working? Could this maybe be an encoder motor problem? Unfortunately, I have a limited OBD2 reader, so it doesn’t tell me about the 4 wheel drive system at all.

 

I would start by checking for any helpful codes per https://blazerforum.com/forum/tech-a...gnostics-7683/