4x4 issue - haven't seen this in other threads

[Plunk]

2004 Ext I6

I've been using the 4x4 regularly this winter (in SD). The other day I backed out of the driveway and couldn't get going on the snowy street so I engaged it. Heard/felt it go and got going down the street. Got out on to the highway and put it back in to 2x. As I did that, I noticed that all the lights on the switch turned on and stayed on. Weird. Then, after the next power cycle of the vehicle, all the lights on the selector switch went out and the Service 4x4 light came on. It's been that way since. I've tried: rotate the switch a bunch, pull fuse 8 with and without engine running, left battery unhooked for a couple of hours (while working on something else). When I do rotate the switch there is no sound from the motors/actuators; I know what the sound is from a previous issue. So, based on all that I've read, I'm guessing my TCCM is shot. What are your thoughts?

 

[Playsinsnow]

http://gmtnation.com/f79/4wd-not-working-step-inside-107/



Try replacing the switch first, after following first step listed above.

 

[Plunk]

Stopped by the dealer and he let me try out a new switch...didn't make a difference. Should I have done more than just plug it in and turn the vehicle on? What's my next step?

 

[The_Roadie]

I suspect the TCCM as well. When lights go out on the switch and the "service 4WD" light on the dash comes on, that usually means the TCCM brain has quit running and the PCM can't communicate to it anymore. I liken it to the "Blue Screen of Death" for our platform.

View attachment 32650

 

[IllogicTC]

The kicker is you can get a ton of scan tools for SES, some of the more expensive ones can also do ABS, but you'd probably need to be hooked up to a Tech II (read: $5000 to get one, or $x for dealer stop) to read the code for the 4x4 lamp. I don't think I've seen a non-Tech II scantool able to read the code behind that lamp, maybe there's one I missed, but it likely would still be a nice penny

But luckily you provided a decent bit of information! I would think TCCM also, especially since it tripped on startup. As far as I know, there's no service 4x4 lamp codes that would be caused by the switch, and the fact it popped on right at startup before you even did anything seems pretty clear. Good luck with it, if you need shop manuals to help with R/R they can be found in the Technical Discussion sub-forum, in a sticky post up-top labeled as such.

 

[Plunk]

Well, found a unit from a junk yard and no luck. Anything special I have to do beyond plugging it in? Any other suggestions or thoughts before I bite the big one?

 

[IllogicTC]

Well, found a unit from a junk yard and no luck. Anything special I have to do beyond plugging it in? Any other suggestions or thoughts before I bite the big one?

I would think since it's come from a vehicle (and therefore came programmed) it's practically plug-and-play. Now I'm wondering if it's a wiring issue, maybe the serial data wire's been screwed up. You can find wiring diagrams in the Technical Discussion page, if you can't view them or can't understand them let me know and I can give you a rundown on the wiring.

 

[Plunk]

I looked through and studied the wiring diagrams. I see all of the connections and what goes where and understand it, I'm just not sure what to do with it. I traced some of the wiring and connectors and there doesn't appear to be any damage. It's snowing and I need to get this figured out...so...ya know...gonna have to pay someone.

 

[IllogicTC]

Just a note:

If it's a serial data issue, it could be literally ANYTHING tied to the data bus. The wiring to all the different modules, or maybe one of those modules spewing garbage on the channel. And in that case, it may actually be best to get it diagnosed, because if it's a serial data issue someone proficient with a Tech II tool could see whereabouts the issue originates.

 

[Plunk]

Thanks for the thoughts, I hear ya. I'm a computer engineer and do programming and actually do serial data comms regularly so I know EXACTLY what you're saying.

 

[Plunk]

Took it to the dealer and got some (lack of) diagnosis. Will you guys please let me know what you think?

Checked codes has codes B2725 ATC Mode switch circuit malfunction, and C0327 encoder circuit malfunction. Test B2725 found atc mode switch failing intermittent needs switch. Test C0327 found encoder motor return voltage is at 4.63 max voltage spec 4.5. internal problem with T-case letting encoder motor over extend. Need to tear down and inspect T-case or replaced. No repairs at this time. Need to teardown and inspect internal transfer case or replace transfer case and needs mode switch -- declined at this time.

Sorry for the lack of grammar, punctuation, etc. I typed it as he did on the sheet.

My concern is that they are saying new selector switch. I already tried that. Furthermore, I actually did a resistance check on the original switch and all positions Ohm out to what the spec is. So, it continues to raise the question in my mind that there is a computer type issue here. Make sense? I'm gonna take it to a different shop for a second opinion.

 

[IllogicTC]

Took it to the dealer and got some (lack of) diagnosis. Will you guys please let me know what you think?

Checked codes has codes B2725 ATC Mode switch circuit malfunction, and C0327 encoder circuit malfunction. Test B2725 found atc mode switch failing intermittent needs switch. Test C0327 found encoder motor return voltage is at 4.63 max voltage spec 4.5. internal problem with T-case letting encoder motor over extend. Need to tear down and inspect T-case or replaced. No repairs at this time. Need to teardown and inspect internal transfer case or replace transfer case and needs mode switch -- declined at this time.

Sorry for the lack of grammar, punctuation, etc. I typed it as he did on the sheet.

My concern is that they are saying new selector switch. I already tried that. Furthermore, I actually did a resistance check on the original switch and all positions Ohm out to what the spec is. So, it continues to raise the question in my mind that there is a computer type issue here. Make sense? I'm gonna take it to a different shop for a second opinion.

Second opinion never hurts. Perhaps there is a loose connector somewhere on the back of the switch or on the TCCM unit. The TCCM generally flakes completely out when it goes, instead of (seemingly) working okay and pointing at other stuff, but who knows? And my thoughts on the mode switch intermittent malfunction is that it may be a secondary fault showing up because of the encoder motor's screw-ups, and may not necessarily be a part of the problem at all.

 

[IllogicTC]

Also, monitor this thread: http://gmtnation.com/f24/seeking-help-4wd-issue-9910/#post221800

It's another guy who has the exact same codes as you.