Many advanced thanks.

I have searched and read nearly every 4x4 thread in this place, and cannot find a situation exactly like mine.

1999 Blazer.
I bought the car for my daughter, knowing it needed some repairs.

The first is a drain on the battery, which was solved after pulling the ATC fuse. Prior to pulling the fuse, I could hear rapid, irregular clicking from the TCCM. I have never had the selector switch light up at all, and never a service 4x4 light come on. Have no blown fuses. Just a dead battery with the ATC fuse installed.

My first instinct was to replace the TCCM. But, since the part is fairly expensive, I figured I had better get some more experienced advice before continuing. Taking it to a GM shop for anything other than a code read isn't cost wise, as I only paid $1000. And its supposed to be a learning experience for my daughter.

So, where shall I start? Anyway to put a meter to the TCCM to check whether its good/bad?

Again, thanks.

 

if youre talking about that little computer on the passenger side in the kick panel. ive gotten lucky before by just taking the connections off and cleaning them if they are nasty, or just di-electric greasing them. sometimes water leaks in there and causes all sorts of issues

its possible the selector switch could be bad too.

 

Yeah, gonna go home and check for corrosion, see what I can do for it, then check the switch.

With the erratic clicking from the tccm, I'm sure its corroded and possibly shot.

I have a bad feeling I'll end up replacing nearly every major part of the system.

I'll keep you all updated.

 

Also helps us to know what type of 4x4 system you have; 3 or 4 button 4x4 switch?

 

I would guess that if you fix the abnormal drain on the battery you will fix some if not all of your problems. Corrosion is unlikely to get you a draw that runs your battery down. Assuming you have a 4-button (with Auto), both the encoder motor lock/unlock and TCCM are on this circuit. Need to get a plan on how to diagnose. May very well be the TCCM, but these are both expensive parts not suitable for unnecessary replacement! Switch is fed electrically by the TCCM and a second fuse - doubt that is the problem. Got a digital volt/ohm meter and a test light? Know how to read electrical schematics?

Again, if 4-button try disconnecting both connectors from the TCCM and monitoring the draw on the ATC circuit by putting a test light in place of the fuse. I you still have a draw the electrical draw problem is in the encoder motor or a short to ground somewhere in the wiring.

Also please be aware that things like a bad encoder motor can also take out the TCCM and a bad transfer case can take out the encoder motor. There are ways to check before spending money, but it is work.

Are you game? Are you committed to fixing the 4WD?

https://blazerforum.com/forum/tech-a...rmation-41198/

 

It's the four button auto 4wd.

Yes I have a digital amp/ohms meter, and can read schematics. I had seen the schematics in another thread, and planned to print them from my desktop.

I was hoping someone with a similar situation would chime in. Maybe start with the components they had problems with.

 

Thanks for the link, Lesmyer.

I see a weekend full of circuit testing in my future.

 

I was blowing the ATC fuse on mine. Problem was encoder motor internally shorted, which as it turned out also took out the TCCM. Lights on 4WD controls always worked, and Service 4WD lit up. Apples and oranges with yours.

You may want to remove the encoder motor and make sure you can click the TC case through it's positions manually with a wrench before spending money on an encoder motor or TCCM. I had to remove the front driveshaft and a corroded-on shield in order to get to the encoder motor. Or if you don't mind gambling a bit, just fix the electricals.

 

Lesmyer,

Would a wonky encoder motor or transfer case cause the rapid clicking in the TCCM while the key is in the "off" position, and the ATC fuse in place?

My guess is probably, because the TCCM is constantly trying to send a signal to the encoder motor to shift in/out of 4wd, or maybe bad wheel speed sensors could do that as well.

Is my thinking correct?

Again, thanks. You're already broadening my knowledge.

 

TCCM should know by 4WD fuse 15 to not try to move the transfer case with the ignition shut off. If the TCCM is clicking with key shut off, and no lights in 4WD switch (which are fed by the TCCM), then I bet the TCCM is bad. In that case, disconnecting the TCCM connectors would make the draw on the battery go away. Question would then be if there was something wrong that damaged the TCCM? Don't believe the ABS is on the circuit after ATC fuse, so not sure how it could be involved. Note that disconnecting TCCM connectors does not disconnect the feed to the encoder motor lock so it could also be a source of the draw.