I have a '99 Blazer with the 4-Button AutoTrac system. Its 4x4 has
been out for some time. I haven't really made it a priority because of
the mild winters we have had in Ohio lately. In any case, I can shift
it into 4HI, but there is where it gets stuck. I can hit the 2HI and
it will blink, and then go back to 4HI. Same for 4LO. I can switch it
to AUTO and it will stay there. To drive the truck, I found out that I
can press the 2HI and 4HI buttons repeatedly and the system will
basically turn off and there will be no lights on the selector switch.
I'm assuming the transfer case is still in 4HI, but the front
differential is disengaged. After a few days it goes back to 2HI and
I'm not sure how or why.
I know from these systems it can be the switch on the dash, the TCCM,
the encoder motor, or the vacuum actuator on the front differential.
The lights on the switch are working fine, so I don't think it is the
cold solder issue that is so common. The TCCM makes a definite click
when the buttons are pushed, but I haven't ruled it out yet. I tested
the vacuum actuator and it seems to engage / disengaged properly. So
everything pointed me to the encoder motor. I took it down, still
hooked up to the wire harnesses and push the selector buttons. It may
a lot of noise, but the key that fits to the transfer case didn't move
at all. I figured it was bad and got a replacement at the junkyard. It
does the same thing so now I'm back to square one.
I do get a Service 4x4 light, but I can't pull the code because it is
the AWD system and it requires the GM Tech2 scan tool. So I can't
ground any pins to read the code. I have tried clearing the codes, etc
and no luck. If needed, I can take it to the dealer to get the codes
read, but I'm trying to avoid their $ervice charge.
I figured it could a number of different issues:
1. The encoder motor from the junkyard was bad as well. (It made the
same noise, didn't move etc)
2. TCCM is bad.
3. Front Differential is actually not disengaging properly.
What do you guys think?