I have a 99 blazer 4x4. Ive had problems with the 4x4. i put a new tcm in and it will shift into 4lo but not 4 hi. I can get it into 4 hi only if i unhook the battery. When i do that it will disengage itself back into 2hi. What could be the problem where 4 lo works no problem. Is the 4hi controlled by something differet than the 4lo.

 

Sounds like an encoder fault. 3-button or 4-button switch in the dash? If it is 3-button, run a search for NV233. If 4-button, search for NV236.

There is a really good thread in the Tech Article (DIY) section on the NV233 both in diagnosis and reading of the codes. The OBD2 Non-Automatic Transfer Case Diagnosis thread will explain how to get the codes from the NV233 system.

 

Is there anyway to reset the encoder and clear it.

 

The encoder is a sensor that tracks the position of the shift sector shaft. If it faults out, you can reset it by disconnecting the battery. The fault will likely return though so this fix would only be temporary and will likely let you down when you most need it.

For further assistance, please let us know how many 4wd shift buttons you have on your dash.

 

I have the 3 button, 2hi 4hi and 4lo. Would that be why when i unhook the battery it works fine for a few mintues then it disengages itself?

 

Very possibly. If that only works for a few minutes, the encoder is likely done for. error_401 posted how he repaired his encoder, but it involved some plastic cutting to get to the thing. But if it's already broke, it'll either remain broke or you'll be able to repair it.

 

Would there have been something wrog with how i put the tcm on? When i bought the truck it wasent working so i put a new one on and here i am.