It's a 1995 and has a 4.3 liter engine and an automatic transmission. I've replaced the vacuum actuator and that didn't fix the 4wd. I've traced the vacuum lines. They are in good shape. I heard of a test where I unhook the battery for 30 minutes to test the TCCM ( Transfer Case Control Module) I did that. If the 4wd worked after 30 minutes, then the TCCM would be bad. The 4wd didn't work. Then the paper said it's probably the encoder motor. Encoder motors are very expensive. I thought I should ask the forum and see if you all agree that I have a bad encoder motor or have see if any other ideas as to what my problem is.

 

I discovered my Jimmy doesn't have an encoder motor. Only vehicles with push button 4wheel drive have encoder motors. Mine has a lever on the floor board to engage the 4wd. At this point the feedback I'm getting from other similar sites is the actuator switch on the side of the transfer case might be my culprit. I've checked all the vacuum lines and they're all good.