Four wheel drive button not working correct

1992 S-10 Blazer. The push button on the dash for four wheel drive doesn't work about 70% of the time. The lights flash when you push it, but that's all that happens most of the time, other times it will go in. Checked dash switch for electrical connection and was good. Replaced electronic module under dash for the fourwheel control. Still same problem. Checked vacuum lines going to tranmission and electrical connections, they are making good connection.

Does anyone know where I can get a diagram and/or check list to trouble shoot this kind of problem? Even better, suggestions from anyone that may lead me to the problem. Much thanks.

Try this one for a start:

http://www.automotiveforums.com/vbulletin/showthread.php?t=572914

Thanks muddog. I had already read that post and tried those checks. It didn't fix it, but the info was helpfull. It seems that the problem I have is a little more in depth and was hoping to avoid the dealer and the $$$$. I'm thinking it's electrical or the encoder motor is hanging. 30% of the time the thing works ok, then zonk! It don't want to work again. That why I'd like to find a diagram for operation sequence.

That info was for 98up and look thru the posts and there is a vac assembly on top of your transfer case that causes many problems on older models - hey all you older model guys help him out on this.

1st Check vac actuator under battery tray for tears, or leaks, and that the vac hose is connected. Replace if found

2nd Check vac hose leading from vac actuator to vac switch on transfer case for cracks and dry rot. Replace if found.

3rd Check remaining 2 hoses from vac switch on transfer case for dryrot or cracks Replace if found.

If all of the above are fine, disconnect your negative battery cable for 1/2 hour then reconnect it. If your 4x4 works after that you probably have a failing TCCM (Transfer case control module)

If that doesn't solve it, it's most likely the encoder motor

Thanks for the info rlith, I ran a check on the vac lines mentioned. I used a hand vac pump and vac guage to test the lines for leaks, also checked actuator the same way. Tested for one hour and vac held. Also checked for collapsed line. I already replaced the TCCM, $$$$, that was done early on. Had to disconnect and remove battery to check the actuator so the reset TCCM was done too.:banghead:

Looks like the encoder motor, eh? I'm down to the big $$ items now. Crap, I was hoping it wouldn't come to this. Have to find one and change it out. I'll post my findings.

what did you find?

i've had the same problem with my 97 4.3L 4WD. haven't had a chance to figure it out completely. the chevy dealer said it was the encoder motor, but not sure how much i trust him. will check actuator and vac lines.

Problem corrected. It seems that the encoder motor was hanging up. Replaced the motor and is working just fine. Thanks for all your help.:)