Here's the deal I drive 1999 blazer 4x4 and I noticed last winter that whenever I transfer to Hi4 mode and turn the wheels the tires vibrate and turns rough. Couple months ago I hit the Hi4 button &it took awhile to transfer from regular mode. Nowlast week I've tried to transfer to Hi4 and it's not working at all.

What should I do? SNOW IS ON THE WAY!!

 

The chattering turn while in either 4hi or 4lo is perfectly normal. Now the slow transfer is not normal, but is pretty common. Does your light just blink then switch back to 2hi? If so, then the TCCM is sensing a fault in the engagement of 4hi and not transferring in. Do you have Auto4wd? If not, then check out the DIY section for the OBD2 Non-Automatic Transfer Case Diagnosis.

Hope this helps!

 

I have Auto 4wd. It used to flash before for awhile then turns on 4Hi, but now it's not even flashing!