4x4 not shifting back to 2hi...

[blair]

I have a 4x4 problem on a 1998 Blazer ZR2 that has me stumped. I can shift into 4hi and 4lo with out a problem. However it rarely wants to go back into 2hi and sometimes will not shift out of 4lo. When I push the butt on the dash it will blink several times and I can hear the transfercase motor actuate, but then it will go back inot 4hi or 4 lo respectively. I've read about many others having 4x4 problems and I've checked or replaced all the obvious one. At least the obvious ones I can think of. So far I have:
- replaced the transfercase shift motor
- replaced the transfer case vacuum switch
- checked the vacuum actuator under the battery - (works good and has good vacuum)
- check fuses
- checked codes at ODB (no trouble codes)
- disconnected the battery

Whats left?????

[vtmecheng]

the only thing left is that button assembly in your dash. I am surprised you didn't find that to be a common problem area on this forum. The box just pops out of the dash and unplugs, there really isn't much more to it. Good luck.

[BlazerLT]

Sounds like a vacuum leak.

Check all hoses for cracks and connections for weaknesses.

[blair]

I initially ruled out the dash panel push button switches and the control module. Both seem to be functioning properly and there are no error codes. When the push button is selected to go into 2 hi the 2hi button flashes, I can hear the relay contact and the transfer case motor actuate. If the switches were bad would the transfer case motor still actuate???

As I understand the system, vacuum is used to engage the front axle and released to disengage the axle. There is strong vacuum at the actuator under the battery and the front axle engages properly. Is vacuum used elsewhere in the system too????

Is there a sensor in the system which may be bad or out of calibration that would cause these symptoms?

As I understand the system, vacuum is used to engage the front axel and released to disengage the axel. There is strong vacuum at the actuator under the battery and the front axel engages properly. Is vacuum used elsewere in the system too????

[blair]

Originally Posted by BlazerLT

Sounds like a vacuum leak.

Good call. It appears to be vacuum related. I pulled the vacuum line off at the actuator and it went back into 2hi once. After that it would not go back into 2hi. Then I plugged the end of the vacuum hose. It worked again, once... Each time I plug and unplug the vacuum hose at the actuator the truck will go back into 2hi once. Why would plugging the vacuum hose at the actuator affect the ability to shift into 2hi?

[s10bajadan]

when you disconnet the vaccume line you say its in 2HI, but have you reached under the truck and checked if the front shaft is turning free. The T-case may still be in 4Hi and the front hubs are just free. When you released the vaccume in the line its unlocking the front hubs only right?

Ive heard the push buttons go bad on the dash as said. Maby You got a bad replacement decoder shifter motor.If its in warrantee maby think about swaping it out with a new one could be on option.

post what happens..

[blair]

Problem Solved.... After changing the encoder motor, vacuum switch, a few vacuum hoses and the push buttons, the problem was finally corrected by replacing the TCCM.

[BlazerLT]

TCCM is the encoder motor.

[blair]

No.

"TCCM" is Transfer Case Control Module.

[BlazerLT]

and the difference between them is?

[blair]

The Transfer Case Control Module is the 'computer' located behind the passenger side kick panel. The Encoder Motor, sometimes referred to as the Transfer Case Shift Motor, is, as the second name implies, the motor that that shifts the transfer case gears.

[BlazerLT]

Thanks, I will add that to the vault of info in my noggin.