I have a 2000 blazer with auto 4wheel drive. When I push the 4hi button it blinks and the "service 4x4" light comes on. About a year ago I replaced the TCCM as it wasn't operating properly. Usually I start testing the 4x4 system this time of year for this reason. I don't want the 4x4 to go out in the middle of a snow storm. But anyways, when I hit the 4hi switch it'll keep on blinking until I hit 2hi again and the "service 4x4" light stays on the duration of the trip until I turn the key off, but once I turn the key back on the "service 4x4" light does not come back on. I'm thinking that the vacuum is ok but I haven't tested it yet. I have searched on many topics related to 4wheel drive and haven't found anything relating to my issue. Has anyone else had this problem? What was your solution?

Thanks

 

I feel your pain. I test mine constantly because every year at the first snow it stops working. It has done this to me for 3 years straight and counting. If the service 4x4 light has come on it has stored a code. You will need to get that read by someone with a good scanner (read dealer in most cases) or you will just being throwing parts at it. There are several things that can and do go wrong with this poorly designed system.

 

I have found that this is now an intermittent thing. I tried it today just before I put into drive and it worked. I hit 4hi and it went right in and I could tell it was working. Steering gets hard while turning. So I took it back to 2hi and tried again and it gave me the "service 4x4" light again and the light kept blinking.

I read an article somewhere that if you ground out pin 13 on OBD2 and turn the key to the on position that the flashes on the switch will blink a code and you can look that code up.