1999 GMC Jimmy 4wd issue

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bigred70

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I have searched several 4x4 issue threads, and I still have had zero luck solving my issue...

My 1999 GMC Jimmy has the 4-button Auto 4x4 panel. Last spring the 4x4 quit working (no lights on the switch). I discovered a blown ATC fuse under the hood. Replaced it, and it blew again. I found several air leaks in the vacuum hoses, and repaired them. Replaced the ATC fuse the 3rd time, and after a TCCM reset (battery disconnected 30 min plus), it seems I have full function of the system and my 4x4 selector lights up (yay!). However, as soon as I shut the vehicle off, the next time I turn it on, the selector lights dont light up and it throws a service 4x4 code.

Here's the kicker...I Molson's bit on grounding pin #13 to read the service 4x4 code on the switch. From what I can see on my diagnostic port, there is no terminal installed in port #13...its empty, along with several other ports.

I just replaced the firewall vaccuum actuator and reset the system...still no change.

Coutesy fuse, 4x4 fuse, and under-hood ATC fuses are now all fine, but still have SFWD light.

I'd like to somehow know what code I'm getting from the SFWD light (maybe just have to bite the bullet and get er scanned).

I need to check for vacuum at the actuator.

Anything else I am missing? Thanks for your help, and sorry I got so long-winded.
 
Q - Did you find out what was causing the ATC fuse to blow ?
 
Not really, but it stopped blowing after I repaired a few broken vaccum hoses. Not sure if that was what was causing it or not.
 
Biggest issue that I can see is that the 4wd lights dont light up at all on the dash...i cant even try selecting a different mode. I replaced the switch and it didnt seem to make a difference. Every time I start the vehicle cold, the lights on the switch flash, but then quickly go away and a service 4wd code is thrown.
 
bigred70 said:
Biggest issue that I can see is that the 4wd lights dont light up at all on the dash...i cant even try selecting a different mode. I replaced the switch and it didnt seem to make a difference. Every time I start the vehicle cold, the lights on the switch flash, but then quickly go away and a service 4wd code is thrown.
Click to expand...

Sorry i been out on tour, the other common issues are the connection at the TCCM which is located on the passenger side kicker panel. The connections there corrode for some reason and can cause the issues you have described.

Check that and keep up the great work, it sounds like you covered most common areas that need to be addressed. Keep us posted and I feel free to post your progress, i did replay to your PM but it didn't go through. :(

Molson02536
 
I just ordered an encoder motor...we'll see if that works.
 
...and the saga continues...

This weekend I took a road-trip with this vehicle (even though 4wd wasnt working). The service 4wd light was on the entire 300 mile trip with no lights on the selector switch.

The next morning I started the car and everything worked PERFECTLY all of a sudden. The service 4wd light never came on, the selector lights worked, and I was able to switch between 4hi, 4lo, Auto 4wd and 2wd with no issues. I turned the vehicle off multiple times and restarted, and everything worked well. I verified that the transfer case shifted by gassing it on the dirt...everything was working perfectly and I was BAFFLED. The big difference I noticed was that right when I turned the key on, I heard the TCCM click a few times, and if that happened, everything worked well.

We took another short 30 mile trip (shopping), and after we got back in the car at the mall, I turned the key on, and the TCCM didnt click, the lights on the selector switch didnt come on, and the Service 4wd light was back.

I'm starting to think that this may be a faulty or inconsistent TCCM, but I'm not sure. The transfer case encoder motor showed up today...is it worth putting the new encoder in, or does this sound like a waste of time?

I'm really scratching my head on this one. I appreciate any help.
 
It would seem to me that you have an intermitent wiring connection somewhere in this circuit. When you took your trip and everything was working is when this bad connection was making good contact. I would start by tracing the wiring from the switch looking at all connectors (even by dis-connecting). Inpect all plugs and wires for any abnormalities.
 
bigred70 said:
...and the saga continues...

This weekend I took a road-trip with this vehicle (even though 4wd wasnt working). The service 4wd light was on the entire 300 mile trip with no lights on the selector switch.

The next morning I started the car and everything worked PERFECTLY all of a sudden. The service 4wd light never came on, the selector lights worked, and I was able to switch between 4hi, 4lo, Auto 4wd and 2wd with no issues. I turned the vehicle off multiple times and restarted, and everything worked well. I verified that the transfer case shifted by gassing it on the dirt...everything was working perfectly and I was BAFFLED. The big difference I noticed was that right when I turned the key on, I heard the TCCM click a few times, and if that happened, everything worked well.

We took another short 30 mile trip (shopping), and after we got back in the car at the mall, I turned the key on, and the TCCM didnt click, the lights on the selector switch didnt come on, and the Service 4wd light was back.

I'm starting to think that this may be a faulty or inconsistent TCCM, but I'm not sure. The transfer case encoder motor showed up today...is it worth putting the new encoder in, or does this sound like a waste of time?

I'm really scratching my head on this one. I appreciate any help.
Click to expand...

Your encoder motor is working so check your TCCM as mentioned earlier and where it is located in your Jimmy.

Good luck and keep us posted.:D
Molson02536
 
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