TCCM clicking does not indicate it is fine.

It seems you may be confusing the operation of the 4WD actuator under the battery. All it does is to use engine vacuum to lock in the front axle when 4WD or Auto is selected. But in addition to doing this, the TCCM must electrically drive the encoder motor to move the shaft in the transfer case in order to drive the locked front axle in a 4WD mode.

So jack up just the right front wheel, start the engine, select auto or 4WD, and try to spin the right front wheel. If you can spin it easily, then this front axle lock is not working. If you can only spin it with GREAT difficulty, then the front axle lock is engaged. Now select 2wd and RF wheel should release and spin pretty easily.

Probably encoder motor is bad, but you will have difficulty diagnosing for certain without Tech2 to command TCCM to go to different positions and to see what position the encoder motor thinks it is in.

One thing to check before replacing encoder motor is the connectors on the TCCM for corrosion. You can clean them and retry if you find corrosion, but it may have already damaged encoder motor from low voltage associated with a corroded circuit. Another thing is to check the 20A ATC fuse in the under the hood relay center - this is used to drive the encoder motor. A third thing to check before replacing encoder motor is to make sure transfer case will click through it's entire range, using a wrench on the encoder motor shaft (with encoder removed).

Forget the 4WD switch as a probable cause - lots of them replaced and few fix anything. You can find instructions on testing them using a digital volt ohm meter in the tech section of this site. When you press different buttons, different resistances equate to different voltages sent to the TCCM on a single circuit. The buttons flash and/or stay on only because the TCCM is driving the lights (not because of anything in the switch).

Final thing to remember is that a bad encoder motor can also damage the TCCM from excessive current required to operate. This was the case with mine (also a 2001 4-button).

Makes you want to go back to levers and lock out hubs, right?

 

VERY true!! This vacuum system only vents from one port to release the actuator for 2wd operation. If the system is tight, it will stay engaged!

 

While I am rebuilding my engine and I'm getting more and more familiar with Blazers, I wonder how many problems had Less went through to get his mastery level...? Couldn't resist... sorry...

 

If you could read the codes that the system has stored It could help you as well but again without a Tech II or a expensive scanner its tough to read them.

 

Lots of problems!! Mostly other people's. Used to turn wrenches in several GM dealerships before I figured out it was no way to make a living and went back to school. But my Blazer has especially been a POS - pretty, but still a POS. If I didn't have so much money in it, I would have stopped fixing it a long time ago. Mastery level - not so much on second gen Blazers because they were after my tenure as a dealership mechanic, but I do know about the things I have been through on mine and what I read here (if it makes sense to me I will repeat it)! Sometimes out of interest in learning and for mental exercise, if I don't have specific experience with a problem I check factory manual and tell a poster what I would do to diagnose.

 

Car Gauge Pro will read/clear BCM/SIR/ABS codes so I imagine it will also do TCCM codes on 1998+ Blazers. It's only $8.95 + $22 for the BAFX Bluetooth OBD2 adapter as sold on Amazon. One of these days I'll do something to set a TCCM code and check it - but that would take extra effort!

I did figure out a way to read the TCCM codes on mine back when I had problems, by manually entering the hieroglyphics to request them in a Scan XL Pro Terminal and interpreting what I received back. But just knowing the codes without having the TECH2 to control the TCCM and read the position sensor on the Encoder motor did little for me.

 

Thanks for the all the relevant info!


I changed the motor 2 years ago, so ima hold off on that till I fix the vacuum problem which is obviously not working.