I've just swapped in an lq9 into my 04 Z71, pulled the harness during the process. Harness was never cut, put it back together just as I believed it came apart, first start I threw no codes except for "service 4wd"... and "low washer fluid" of course. So it runs and drives fine, but 4wd will not engage (I have the electronic buttons) and it continuously says "service 4wd". I've traced back the looms trying to find a plug, but I'm 99% positive I got them all. There can't be more than one or two plugs on the engine harness that even relate to the 4wd. Anyone have some insight?

 

mine was doing that and then eventually wouldnt say anything. ive bought a new shift module, and new push buttons and what the guy at the dealership told me is the tcm could be in sleep mode?

 

Hey Will. It's a long shot but I think that one of the plugs that goes into the transmission is the same as the one that goes into the transfer case. Maybe you got them switched. I kind of doubt it but it's worth checking.

 

Yeah I got under there last night and looked around I couldn't see any plugs that would reach anywhere else, everything seems to be in its own spot. I'm glad everything else is working correctly, but this issue is really bothering me.

Thanks again for the time you spent last night tuning, that 6.0 really came to life.

 

Code that it is throwing is C0379. Most of the searches I have done say to just replace the actuator, I've found really good prices on 1aauto.com. Anyone know of any other possibilities before I order?

 

I've been wrong before, but I would say that if the 4wd actuator was working before you started messing with your truck (engine swap) then something that you did caused the 4wd to stop working.

 

this may sound dumb but i bet your TC module is in sleep mode... you have to take it to the dealership and they can " turn it back on' its like 50 bucks or sumthing let me know if this helps...

 

this may sound dumb but i bet your TC module is in sleep mode... you have to take it to the dealership and they can " turn it back on' its like 50 bucks or sumthing let me know if this helps...

 

No such thing as sleep mode on a transfer case module that it can get stuck in. Find a trouble tree for the code you have and follow it through. You will figure out in short order if the actuator is bad or a wire thats broke inside the harness.

These late model gm harness' suck when you disturb them after they get some miles and age on them. The wiring is so crappy it work hardens in one spot and then when you wrench it around all kinds of damm gremlins show up that were not there in the past

 

You can discount the two speed sensors on the back of the case. They won't cause the Service 4wd to come on (I screwed up once and wired these two together, it causes no speedo and ABS light to come on. I'd double check the harness that comes off the T-case that I believe powers the actuator.