2001 Chevy s10 4WD Problem

Hello All, Here is what's happening...I'll be driving in 2wd and all of sudden the 4wd will kick in without pressing the dash button. This started during this past summer and is now happening more often. I am also now hearing a noise coming from the 4wd on occasion sounding and acting like it is between 2wd and 4wd. I can stop the noise by cycling the dash buttons from 2wd to 4wd and back to 2wd. I'm not sure if it's the accuator or something else. Anyone have any experience with symptoms like these? Any advice or help is appreciated!!

To start with the easiest things first try disconnecting the switch. Pry it out from the dashboard and disconnect the plug from the back and see if it still happens. If it stops you know its the switch if not probably the module.

Found the problem! I replaced the Transfer Case Vacuum Control Switch. It is located on the transfer case and has 3 vacuum lines going to it. Cost $17 and took 15 min to change.

There are two of those switches available from the dealer. The original switch, part no. 15664811 had a problem of letting transfer case fluid get into the vacuum lines and really mess up the AC/Heat controls. It had a green inspection mark on it.

The revised switch, part no. 89059420 solved this problem and had a blue inspection mark on it.

I don't know if any aftermarket switches are available.
Which one did you get?

Also, Mine did not have the o-ring on it from the dealer. I had to take the o-ring off the old switch to put on the new one.

James