Not to beat a dead horse about Blazer 4x4 not working but I have encountered a strange problem with my 1999 Blazer. I have checked all the vacuum lines, replaced the vacuum actuator and the t-case vacuum switch so that I now have it working.

I have the 3 button switch and I have verified the right front wheel engages and disengages while on jacks. This is my dilemma:

I have discovered I can engage into 4 HI and back into 2 HI only 6 times before it quits working and stays "stuck" in 2 HI. The switch lights illuminate properly. No blinking.

Oddly, when it stops working after the 6th attempt, I pull my courtesy lights fuse and put it right back in, it seems to "reset" something in the system and I'm good for 6 more cycles from 2 HI to 4 HI. And always just 6 cycles.

But at anytime during the 6 cycle limit, if I put it into 4 LO, I can't get it back into any mode unless I turn the ignition off or pull the courtesy light fuse again. In other words, 4 LO will engage and work properly (steady light on the 4 LO button) until I try to shift back to 4 HI or 2 HI. I will have none of the button lights illuminated when this happens and it is "stuck" in 4 LO.

Any thoughts?

Rick

 

Have you checked the contacts on the TCCM to make sure they are clean? You can also unhook your battery for 10 minutes to reset the system. Not sure why you have a "magic number" of 6. Usually when its random I look at the TCCM contacts first.

 

This may be related to the "magic number" of 6 (from the service manual):

During electronic shifting, the TCCM monitors the transfer case encoder circuit for the proper
operating sequence. If at any time during a shift, the encoder changes from one position to any
position other than the next possible position, an error counter in the TCCM increments by 4.
After the counter reaches 32, the transfer case shift control module set a DTC 2, a permanent
"encoder fault," and reverts to a 2HI to 4LO or a 4LO to 2HI shift pattern only. To guard against
a transient, random encoder fault due to vibration, dirt, electrical noise, etc., the fault counter
reduces by one each time the TCCM detects a valid encoder value. The encoder must
intermittently fail 25 percent of the time for the transfer case shift control module to consider
it faulty and store DTC 2. It is imperative that the technician test-drive the vehicle and request
several shifts in order for this code to properly be set.

Still seems like 6 is an odd number, though. You'll probably want to do the diagnostic testing procedure of the TCCM and see if you get a DTC 2. My edited version of the procedure can be found here or you can check out the DIY section.

 

Encoder motor faults tend to be line this. It's either the encoder having an issue or the TCCM having an issue. Check terminals, if I had to pick one i would say encoder motor. I see those fail more than the TCCM.