My 2001 BlAZER keeps jumping to one of the 4 wheel drive modes from 2 wheel drive. My guess is a problem with vacuum lines, but not sure, Any help would be greatly appreciated.

 

Do the lights on the switch indicate that it's changing modes too? I know they have a problem with contacts inside them, usually just makes the lights in the switch not work, but anything's possible when you bring flaky electronics into the question...

 

My 98 did this around 5-6 years old. The 4x4 computer is in the passenger kick panel. Remove kick panel and the computer. You’ll need a soft brass wire brush (tooth brush size, electronic sensor cleaner ( use sparingly), and a cutting torch tip cleaning tool. Very very carefully clean the connections in the tcase control module with the brass tooth brush, and maybe a custom bent eyeglass screwdriver to scrape green ugg off the tiny prongs that have corrosion. Use the torch cleaning tools to clean inside of wiring harness . You will probably have to clip most of the smooth part of the end of the cleaning kit to get the ridged part in the connectors far enough. !!!!!!!!!!!!!!DO NOT USE TO BIG OF A TIP CLEANER!!!!!!!!! IF YOU DO YOU RISKING CREATING A LOOSE CONNECTION!!!!!! Once you’ve done this use the electronic sensor cleaner and spray plugs out. If you do this to the control module use very little pressure and do it upside down to keep chemicals out of module or just use air . Use air to blow plugs out to speed up drying process on plugs if you’d like. Remember the control module is delicate don’t blast it with 125 psi at point blank range.

 

The light do change.
Thanks