Hi everyone, I am having a very hard time with the push button 4x4 on my 2000 chevy blazer LS 4 door 4.3l with auto trac i believe its called (4x4 auto). I have diagnosed that the vehicle is in 2hi when it is in park, upon ignition it shifts into 4hi and will not come out. I can get it into 4x4 auto but the front dif is still engaged. After doing some research i decided that id replace the TCCM. I have tried 3 modules and none have solved my problem, But each one did do something different. One of them shifted though the gears but not corresponding to the button pushed. Thus i don't think anything is wrong with the mechanical system itself, I believe the problem to be electrical. After looking into the problem further it appears that the previous owner hit a rock or something off the Tcase. I noticed that the skid plate was bent right where the encoder motor is. Does any one know if there's a chance that a good hit could mess up an encoder motor? Could my wiring be bad? Did i receive 3 bad TCCMs? Any help would be highly appreciated. Thank you

 

I would test the resistance through the dash switch both at the switch itself as well as down at the TCCM to see if it is giving the proper feedback to the TCCM. If the resistances are off, the TCCM won't know what to do. The resistance values are listed in the Tech Article (DIY) section 4wd related post.

And just for clarification, the front axle will be engaged in all 4wd modes, including Auto 4wd. When in Auto 4wd, only the output to the front axle is varied depending on traction conditions. It can vary the output from basically zero torque transfer to the front (just what the friction clutches have for preload torque transfer) to full lockup providing full 50/50 torque split front/rear.

 

Got another blazer recently, logged back on and saw this post.

For anyone who cares i actually got another TCCM and it solved the problem. They are known to fail and many faulty ones get sold out there. Took me 4 to get a good one. Make sure you buy from someone reputable.