I have a 1996 GMC Jimmy that I was planning on using for Winter driving in Wisconsin. It seemed to be working fine and then half way home from work the 4WD stopped working. The buttons and indicator lights on the dash indicate that everything is working fine, but it clearly isn't. No power to the front wheels. I'm hoping that its either a vacuum actuator problem, or the vacuum switch on the transfer case, but it seems weird that the system thinks the front is locked in when its not.

Any thoughts????

 

I don't think the 4wd system "knows" whether or not the front axle is engaged or not. It only knows if the instruction has been given or not. So it is likely the vacuum mechanism could have failed.

 

Thanks. I wont be able to look at it until tomorrow. I'll let you know what I find.

 

BTW, is the HVAC system working correctly? I ask becuase if there is a vacuum leak "upstream" toward the engine then that can affect bot the HVAC and 4wd engagement.

I had some of my vacuum lines rot and cause the HVAC system to not run correctly. It was during the summer when I don't use 4wd much so I did not notice the problem from the 4wd not engaging only from the HVAC not working.