Ok so quick back story.. I have been having issues with the 4wd getting stuck in 4lo randomly and on its own and being extremely difficult to get out of.. ive also had it get stuck in neutral and came across the TCCM reset which has helped a few times now. I also know the plugs on the TCCM itself occasionally corrodes, With that said, about 2 moths ago it did the random shift to 4lo and I just couldnt seem to get it back into auto or 2hi until very recently i tried the reset and eventally got it to disengage. I looked into getting a used TCCM but realized that it may not work because of needing reprogrammed, and that is when i decided pull the 2 main fuses controlling 4WD (the 4WD labeled one from inside teh vehicle, and the ATC labeled one under the hood), unplug the TCCM and clean the contacts.. which the black plug was a little corroded..

I left it unplugged and all fuses out for at least an hour, then plugged the TCCM back in, plugged the ATC fuse in and thats when i started hearing the clicking sound and realized it was coming from the TCCM, i also noticed the security light blinking, and this was with no key in the ignition.. I removed teh ATC fuse and the clicking stopped.

I decided to check again today this time with the 4WD fuse in and I turned the key to on but no attempt to start it mainly because I have no clue if it will do something worse. Could teh TCCM have died just from me unplugging it and spraying a little bit of electronic cleaner across the plug contacts, or am i missing something here and its a easy thing to reset.. As of now the 4WD/Neutral indicator lights on the buttons all blink with the key in the pre-on position (not started).

Im curious if it was engaged in Auto 4WD before all o fthis started happening, if i can drive it normally without the TCCM/4WD fuses in, at least temporarily as i kin dof need it to move in the next couple of months, or if its at least safe enough now to have it towed since 4wd is no longer engaged. Preferabbly id like to fix it.. would replacing the TCCM fix it, or could it be a problem with the black plug on the wiring harness (I'm assuming that's the plug supplying power) while the orange(maybe blue, i forget) plug is all of the "data" lines..

Or am i totally overthinking this and just need to start the vehicle so it recognizes the TCCM, like as in the length of time it was unplugged completely reset it.. Yes im a bit of a newbie/idiot when it comes to working on vehicles.. Put me in front of a broken computer however, and i prob fix it,, lol

 

I should also note that i replaced the vacuum lines (i think last year) which were a problem as well. Which fixed some of the random switching and being unable to disengage 4Lo problems for awhile, until say maybe the last 6 months and it started doing the random shifting of 4WD again.

 

The TCCM is likely just going bad. I had to replace mine in my 1999 about 10 years ago. There was no programing of it involved. Just be sure to find the compatible part numbers. A search of the online GM parts retailers, especially the ones for which you input your VIN, can help you track down the original part number and any that have since superseded it.

The clicking you hear is the reed-relays trying to work. You should only hear them click once and normally they are hard to hear.

If you are in Auto 4wd, you should be able to drive around just fine. I believe the owners manual suggests not to do this as your mileage will not be as good as when you are 2wd. I'm assuming you are in Hi not Lo.

Replacing the vacuum hoses is a big help. It is important to do them all.

 

So could i technically still drive the truck without the transfer case control module, like totally unplugged and fuse pulled. Or could it being engaged in Auto4WD cause it to potentially shift into a 4 low/hi or is it being auto 4wd mean its technically in 4h and can auto shift to 4 lo... And does it being in auto4wd mean it cant be towed unless its on a flatbed.. If i have to have it towed and i cant get it moving just without a 4wd option, at least temporarily

I was going to try to turn it on with the fuse unplugged, whihc im thinking will be fine.. I guess shifting is where it might all go to **** potentially

 

The Auto 4wd feature engages clutch plates in the transfer case, switching it from 2wd to 4wd when it senses wheel slip. When the slipping is done, it puts it back into 2wd. Whether it is in Hi or Lo is different. If it is staying in Auto 4wd and operating as intended while in Hi, then it should be ok to drive.

On dry pavement, say in a large parking lot, when doing tight turns do you feel any binding or skidding of the front tires while executing such a turn? If yes, then you are stuck in 4wd. If not, then it is operating in 2wd. The question is will it stay in 2wd and only go into 4wd when it should. If the answers are yes, then it is ok to drive. But I would not go on any long trips and only drive it locally where you could stop driving if you immediately feel binding.

I'd suggest you might call a local transmission shop and confirm though.

 

Thank you.. i think another concern would be it doing the old getting stuck in neutral trick and then having to do the TCCM reset (pull ATC fuse, wait 30, turn key on/off 5 times, etc)..Im guessing that isnt something to worry about if the TCCM is not in operation, an dif it happens then it means it possibly/probably wasn't just the TCCM.. Again thanks, not knowing keeps me from trying stuff most mechanics are prob like .. whta the hell. just try it and see what happens.. LOL

ohh i just now realized i read your vac line thread when i replaced my vac lines.. :-)