Switching in and out between 2WD & 4-Hi in my 2005 Jimmy (3-button) has been unreliable at best.

Right after I bought the Jimmy in 2007 I had a used encoder moter swapped in. When that didn't solve the problem, I had a used TCCM swapped in last fall. All worked fine until recently.

Now the same old symptoms are back:
-Shifting may take 2 or 3 pushes of the button (you hear the encoder motor trying to shift, but it doesn't always lock in);
-Sometimes can only shift if in neutral;
-Sometimes I push the button and nothing happens whatsoever. So I shift to neutral, push button and only get blinking lights;
-When all else fails, I unplug the TCCM, wait a minute or 2 and plug it back in. All will work fine for a day or 2, then back to the same old problem.

Last year I had the GM dealer look at it, but he wants to put in a new encoder motor for $1200, based on the following diagnosis:

"CAUSE:
SCAN TEST, CODE DTC002, VOLTAGE TO ENCODER MOTOR OK, ON CIRCUIT P,A.B.C. (501 volts) TEST GROUNDS, OK, POWER OK

CORRECTION:
CLEARED CODE, WORKED TWICE THEN WOULD NOT SWITCH MODES, SWAP MODULE WITH GOOD MODULE, REQUIRES ENCODER MOTOR REPLACED."

Given that the encoder motor was previously swapped, I'm not so sure that's the problem.

I feel like everybody (GM tech included) is just guessing and swapping out parts. Surely this can be fixed. HELP!!!

 

There is plenty of information on the NV233 transfer case (what you have) here. Your symptoms are classic encoder fault. Nothing new.

The fact that you installed "used" components does not absolve those components from fault. It is just a cheaper alternative that may not pay off. In this case, it bought you 2 years.

Unplugging the TCCM will work for awhile until the encoder really fails then you will be SOL.

If the connections at the switch in the dash, the TCCM, and the encoder motor look good, then the encoder is the likely fault point. You can test the channels to see what is really going wrong, but the encoder is not independently serviceable. error_401 wrote a good write up on the NV233 transfer case and its controls. Almost all of it applies for all of the vehicles using this transfer case regardless of 1st gen or 2nd gen.

 

Thanks Swartlkk! I found Error-401's post and it explains a lot of things!