I have a 2004 Blazer 4x4 with 3 button TC control.

Problems I am having are varied. When shifting from 2H to 4H, it works about 50/50. When it doesn't work, I get the 4H to light when I push the button, but it doesn't shift to 4H. It just reverts to 2H again. Sometimes when it reverts back to 2H, no lights are on, but not always. When no lights are on, I can always stop and put it in neutral and push the 4L button and get it to shift into 4L (with both 4L and 4H lights on). I can then push the 2H button and get it back to 2H, but not 4H. After this, no buttons work again until I disconnect the battery and reset the TCCM. After the reset, the cycle will continue. Sometimes I can get it to work normal maybe 4 or 5 times. Also last time I was in the snow, I put it into 4H then looked down and noticed it had switched back to 2H on its own.

Things I have done:

Replaced the button assembly 3 times

Replaced the TCCM

I am wondering how the TCCM knows that the TC has shifted?
Is there a prox or limit switch somewhere?
If so, is it inside the TC or external?

Thanks in advance for any advice.

 

What diagnosis was done to determine that either of those items needed to be replaced? Are there any stored codes in the TCCM? Have you looked at any of the NV233 threads in the Tech Article (DIY) section (an index of which is linked to in my signature below)?

The encoder portion of the encoder motor is what relays the position information of the transfer case shift sector shaft to the TCCM.

 

Just reporting back that after reading the suggested threads, that jumpering pins 4 & 13 on the OBD-II plug that I bought, indicated that I had an encoder problem. I pulled the plug from the encoder and checked the pin voltages and ground continuity. All checked good, so had to assume that it was the encoder itself. Bought a new one for $180 and slapped it in and everything works great now. Thanks to the knowledge base in this forum I saved a few bucks. On my '04 Blazer I had to remove the drive shaft to get the encoder out. Just not enough room otherwise.

Thanks again.

 

Thanks for the feedback! Glad you got it all fixed back up!