I have a push button 4 wheel drive setup on my 99 silverado that ive been trying to figure out why the 4 high wont lock in the front axle. But if i put it in AUTO 4 wheel drive the front axle locks in fine. I have already replaced the push button module on the dash and still no luck. I recently picked the truck up and put it on jack stands. With it off the ground If i press 4x4 high the front wheels spin. But with it on the ground i can tell they arent locking in. I live in Michigan and its snowing here so its easy to tell if your four wheel drive is working or not. I have no warning lights or check 4 wheel drive lights. Any one have any ideas hopefully. On these trucks are the front cv axles suppose to always engauged even in 2 wheel drive.

 

I had a ton of problems with my 4x4 system last winter. I replaced the switch, and that didn't do it. The next cheapest option was the t-case encoder sensor, and that did the trick. It was like 88 bucks from AutoZone

 

I tried replaceing all of the sensors on the t-case as well. There are 3 of them. One on the in the input shaft. The one on the front output shaft section going to the front diff and the one on the rear output shaft going to the rear diff. They were all fine. Im thinking maybe my t-case cluthes are burnt. It just makes no sense because it works fine in auto four wheel drive.