Hi guys, my son recently purchased a 2002 ZR2 Blazer, yesterday he put it in 4wd, now the only way to get it back to 2wd is to turn the ignition on/off a few times then press the 2wd button, it takes 3 or 4 attempts to get it into 2wd but it will eventually go in, it will not go into 4wd-Lo.
The Transfer Case Shift Motor, vibrates and buzzes real loud, and the 4wd service light is on, my question is does does this problem sound like its a bad Transfer Case Shift Motor, anything else that could be causing this problem, I have read as many posts as I can about 4wd issues on these trucks but would gladly receive help on this question.

Thank guys and have a great 2012..

 

Last spring I repaired almost the same thing on my uncle's S10. His shifting problem was caused by a broken gear inside the transfer case encoder motor. Every once in awhile the full teeth of one gear would mesh with the semi-broken teeth of the gear attached to the shift sector shaft on the transfer case and allow it to shift.

Have you tried monitoring the encoder channel states to see if the encoder motor is actually changing the position of the shift sector shaft? Details are in one of the NV233 tech articles.

 

Thanks for the quick reply, no I have not monitored encoder channel states, dont know how to do this, I do know that when it was in 4WD Hi, it was actually in 4WD Hi, I jacked the front end up when in 2WD and the front wheels are not turning when in drive so its in 2WD.

I`ll do a search for the NV233 tech article..

Hi swartlkk, you couldn't link me to a how to for monitoring encoder channel states, sorry I cant find the info for myself..

He has the 4 button switch, should this be in the NV236 tech articles

 

Since you did not mention the Auto4wd function, I assumed a 3-button NV233. Shame on me for not typing out my standard reply I guess.

With the NV236, you can test the wiring, but to do any further, more advanced testing, you'll need a full feature, bi-directional scan tool (Tech2 or equivalent).

 

Just to update what I did to fix my sons 4wd issue:
I tried a new Transfer Shift Motor, this did not fix his issue, next a took a look at the shift control module, this was heavily corroded and a pin inside the harness had broken off, to fix this I opened up the control module and soldered a wire to the broken pins leg, I fed the wire to the outside of the control module and soldered it to the corresponding wire in the vehicle harness, everything now works great.