Hey guys, I have a 4 button 4wd on my 99 Blazer. My 4wd is completely non-working, and it boggles my mind why. I push the buttons and NOTHING in any way shape or form happens. No noises, no lights changing, nothing. Let me give you guys some background on what is happening and what I've checked. First off, it is lighting up the "service 4wd" light on the dash. The back lights for the lettering on the 4wd dash switch light up, but the indicator lights do not, no matter what I do or press. I took the switch out and tested the resistance and everything is perfect in that regard. I checked vacuum to the vacuum switch above the distributor, and the line that goes on the bottom has vacuum, the top one doesn't. Is this correct or is it backwards? When I bought the Blazer in March of this year the guy told me the TCCM was bad and that was what was causing everything, so I took his word for it and bought a new one, still didn't change anything. I cleaned all the terminalls at the TCCM with alcohol and WD40 and packed them with vaseline. Still nothing. My only remaining guess is that one of the wires at the TCCM is not getting power or is broken, but I don't have a diagram or schematic for that to test voltage. Does anyone have that schematic/diagram? Any other ideas on what could be causing this? I'm open to any and all sugestions.

Thank you in advance,
Nick

 

Since you had another thread a few months ago concerning your 4WD issues, anybody wishing to reply to this one might want to read it, also.
Original thread: Bad TCCM???

 

Yessir, still fghting the same issues, but since I know the TCCM is good, I figured I'd start a new thread and add some more detail

 

bump!

 

Seriously? No one? Some one has to have the wiring schematics at the very least?

 

If you've read any other threads about problems with the NV236 Auto-4wd transfer case, you would have read that you need to have the TCCM scanned for codes with a Tech 2 or equivalent full function scan tool. That would be the first place to check. Your truck is trying to tell you what's wrong by illuminating the "service 4wd" light.

 

I did. It won't connecet to the TCCM to read it (it has no issues cunnesting to the ECM and reading/clearing engine codes). I've even used 3 diffrent tech 2s. Sorry, that info was in my original post that riddle posted up, I forgot to mention that in this thread.

 

Are you sure they are going into the proper screens in the Tech 2...? It is not under powertrain diagnostic. You have to go under the chassis section I believe.

Anyway, have you tested continuity from the switch in the dash to the TCCM? Have you verified that the TCCM that you purchased is proper for your application?

 

Hmmm, that I can't tell you for sure. I went to a reputable all around service center, a Chevy dealership, and a GMC dealership, so I'd hope at least 1 of them accessed the correct screen. I'll see if I can't get my hands on a Tech2 from the automotive tech center at school.

I unfortunately do not have the wiring diagrams/schematics to know what wires to test, otherwise I would.

Part number that is on the TCCM is 12577412. I believe this is the correct part number/unit for the application?

Thank you so much for the replies/help thus far! I greatly appreciate it.

 

The link in your previous post (CLICK HERE) has the wiring diagram for the switch to the TCCM. That post also lists the resistance values for the switch when each button is pushed.

Here are the main connector pinouts: