I have a 2000 4 door Blazer that works fine somtimes but more often than nt the 4x4 service light is on. I have read through many of the threads and have used many of the troubleshooting ideas with no success. Sometimes the 4x4 systems works just fine. Start up the Blazer the 2W light is on can switch between 4H and 4auto without the 4x4 service light on. Then later the same day start it up and none of the 4x4 selector lights are lit and the 4x4 service light is on. Other times it works fine, can switch between 2x, 4x, and 4auto but as I drive down the road the 4x4 service lights comes and it gets stuck in 2x (some times with 2x light and sometimes the light is off). I have performed the following trying to troubleshoot.
1.) Checked vacuum hoses
2.) Front axle acuator and cable to axle work fine
3.) Checked electrical connections at encoder moter TCCM, vacuum switch on fire wall. All looked good with no corrosion.
4.) When I checked the axle vacuum acuator the battery was disconnected for 30 minutes and when I reconnected it the 4x4 work for two full days without any issues. Generally it does not work consistantly for that long of time.

I'm puzzled as to what parts to replace seeing that at times it works without issue. Recently I noticed that it's more proned to work if I slowly insert and turn the ignition key. Could all of these symptoms be caused by the ignition switch? Any ideas would be appreciated. I took it to a local garage to check the error codes but they charge $90 to check the codes and I do not have that kind of money just to see what needs to be replaced, so I'm hoping I can troubleshoot without spending the $90.

 

I don't know where you're from, but autozone, advanced auto parts, etc will read codes for free.

 

Reading the codes really is the first place to start. The TCCM has stored codes which will likely lead you to the source of the problem.

From your description, it sounds like you are experiencing an encoder fault. When this type of problem typically starts, a reset of the TCCM by disconnecting its main power can result in a functional system until it senses the fault again which may take some time.

Autozone/Advanced Auto/etc may not be able to read the TCCM codes. It takes an enhanced scan tool to access that system and others like it (SRS, ABS, etc).

 

Thanks for your response. I did go to Autozone, but they do not have the ability to scan codes for the 4X4 system. The associates at Autozone directed me to the repair shop that charges $90.