Why won't a 1999 GMC Jimmy engage into 4 wheel drive when the selector button is pushed and the 4 wheel light is on?

Answer 1

It could be one of two things:

A fuse

OR

The 4 wheel drive actuator

There is actually a 4x4 actuator that costs 120.00 at the dealership and 50.00 at your local auto parts store. That tends to go out if you do not use your 4x4 more than a couple of times a year. That actuator uses a vacuum line to move and shift the gearing or assist in it. The problem I had (and its the same with push button or manual shift transfer case from what I was told by Chevy) is that when I shifted into gear, it sometimes wouldn't go for a while. And sometimes it would even shift into 4x4 without me shifting it into the 4 wheel Hi setting. I replaced the actuator with the Schucks part and it works great now.

Its under the battery tray (the battery tray is held down by 4 screws, 3 in the top part of the pan where the battery is, and one screws into the pan from the wheel well). Pop that off, and you see the actuator. Its got a diaphragm with a wire going into the center, and on the bottom of the side of the actuator is the vacuum line. disconnect that vacuum line first so its out of the way. For the wire that goes into the actuator, there is a pin holding it in place. remove the pin (it holds the wire in place) and then its free to remove (once you remove the screws from the back of the actuator, there are 3 of them, and I think they are metric if I remember right).

Now when you re-install it, screw it back onto the mounting plate first so that it wont move around on you. DO NOT FORGET TO INSTALL THE VACUUM LINE IF YOU DONT INSTALL IT NOW, that would be a pain in the butt to deal with later. That pin that comes on the metal part in the notch on that diaphragm needs to actually go INSIDE the notch and pushed until the pin will hold that wire in place. Look at how the old one was in place and shove it in the notch the same way. Its a little bit hard to describe, but there is only one way that end of the pin can go into the notch so that it holds the wire in place when you shift that gear. MAKE SURE its in secure (it will be held in by itself where the pin is about in the middle of the hole so it catches and holds on the notch in the cable and wont actually come off when you insert the cable, they hold themselves in pretty well and wont come out). MAKE SURE THAT VACUUM LINE IS CONNECTED. Re-install the battery tray and battery, and fire up your car and push the button.

If the fuse did not work, then its probably this actuator. Good luck!