"service 4wd" When I Go From Auto 4wd To 2wd

jbeall · December 22, 2009

Howdy,

I've got a 2003 Yukon XL. I don't use the 4WD mode much, but lately we've had a lot if ice and snow and in our neighborhood there is still a lot of ice. You have to drive slow and there's plenty of slipping and sliding. I put it in Auto 4WD because based on my understanding of the different modes (Auto 4WD, 2WD, 4HI, 4LO) that is the most appropriate for variable conditions like icy roads that may have some exposed pavement.

My DIC is now giving me a "Service 4WD" message when I go from Auto4WD to 2WD. The manual for my vehicle describes this error message as follows:

If a problem occurs with the all-wheel drive system this message will appear on the DIC. If this message appears, stop as soon as possible and turn off the vehicle. Restart the vehicle and check for the message on the DIC display. If the message is still displayed, or appears again when you begin driving, the four wheel drive system needs service.

So, I turn the vehicle off, and turn it back on again, and the error disappears. Until the next time I go from Auto4WD to 2WD... so what's going on? Any suggestions?

-Josh

jbeall · December 23, 2009

Can I scan for codes on this with a regular ODB II scanner?

I have a friend that has one I could borrow, and Autozone will do a scan for you for free. I'll be out tomorrow, I could stop by Autozone.

alwcurlz · December 23, 2009

Could be a number of things. Plugging it into a scanner would give some clue as to where the problem is. Those small scanners don't say a whole lot so you may have to take it to a shop and have them diagnose it on their system. My first thoughts on this would be an actuator malfunction.

jbeall · December 26, 2009

Well, it got better (it stopped saying "Service 4WD" after I went in/out of Auto 4WD/2HI), and then it got worse just tonight. Merry Christmas, eh? :-)

We were out today visiting family for Christmas. I got the "Service 4WD" message after I switched from Auto 4WD to 2HI, and unlike the previous times, when I turned the engine off and then back on, the message did not go away. Additionally, the lights on the transfer case buttons were all off (normally it has a light next to the mode you're in--e.g., Auto4WD, 2HI, 4HI, or 4LO).

Fortunately we were close to home, and so I decided to just drive home and check in with the local dealership tomorrow morning (if anybody is there). On the way back home, at about 40mph, I suddenly started getting a rattling/grinding sound--just as I noticed the light next to "4LO" came on. I immediately put the transmission in neutral and slowed down to a stop, then hit the 2HI button. It clanked once and then all returned to normal--no more grinding sounds, and it felt normal when I lightly stepped on the gas to accelerate back up to speed.

I drove it the rest of the way home and I will check in with the service station at the dealership we bought it from as soon as I can get ahold of somebody... hopefully nothing got seriously damaged :-(

Naturally, I'm interested in any feedback on what could be up. A failed actuator sounds like a reasonable guess. Any other suggestions? And also, any input on what I should tell the technicians who will be looking at it.

-Josh

gmtech4 · December 26, 2009

you tell them what you wrote here ,do not give any diagnoses at all ,its not for you to tell them whats wrong,its the other way around ,that what you pay them for,if you give a diag and they look for that ,they have an out when it blows up in your face ,ya read me ?NEVER EVER GIVE A DIAGNOSES!!

merry xmas

besides ,if a customer told me what to look for I would say "who is this guy suppost to be ?"

remember the all mighty male ego lol

good luck

alwcurlz · December 26, 2009

Well Josh, one suggestion I could make would be to try re-flowing the solder on the circuit board of the control panel for the 4WD. The main leads that run into board have been known to develop a cold solder joint situation caused by the weight of the wire harness hanging on the backside of those extending pins. Shouldn't be an issue on a later model as you have but, it's worth a try and not expensive. I did that to my control panel and it fixed my "service 4WD" message.

alwcurlz · December 26, 2009

you tell them what you wrote here ,do not give any diagnoses at all ,its not for you to tell them whats wrong,its the other way around ,that what you pay them for,if you give a diag and they look for that ,they have an out when it blows up in your face ,ya read me ?NEVER EVER GIVE A DIAGNOSES!!

merry xmas

besides ,if a customer told me what to look for I would say "who is this guy suppost to be ?"

remember the all mighty male ego lol

good luck

Don't worry about that Rob. Just handle it like I've done in my own experience. Listen to customer ideas and other suggestions, nod your head, give the uh huh, yep, and realize they wish they could fix it themselves and can't. Empty your brain of their written report and/or verbal advice and then look for the problem like they didn't say or write anything. Then once you've found the problem, tell them what it is and point it out. Fix it, and you're done. Works for me every time. That's the one thing many technicians have a problem with, not ignoring the customer and using experience/training to find the issue. After all, why are they there in the first place? Some people come by and say: "It don't work right and goes cling cling; is it my muffler bearing?" What do you do then?

jbeall · December 26, 2009

I talked to the owner of the dealership where we picked it up this morning. None of their technicians are in today (I can hardly blame them, it's the weekend and the day after Christmas :-)), so we'll have to drop it off Monday morning to get it looked at.

I described the problem to him and his advice was, in essence, that we can drive it if we need to, but leave it in 2HI (don't switch to any of the 4WD modes).

JTJohnson17 · December 30, 2009

I have had similar problems. Looking around under the hood, I noticed that the ground strap from the hood to the firewall was broken. I replaced that and it seems to have cleared up the Service 4WD error code that I was getting.

Worth a shot to check.

Jeremy

jbeall · January 12, 2010

The dealership I took it to said it was the "encoder sensor" that controls the motor that moves the transfer case into the various different modes.

It was $100 for the part and $120 labor for the repair (total $220, plus sales tax, which they charge on everything here in WV...).

It's been several weeks and so far so good...

Was that price fair? I didn't really have time to shop around, I needed my truck fixed.

Nytemare · January 12, 2010

The dealership I took it to said it was the "encoder sensor" that controls the motor that moves the transfer case into the various different modes.

It was $100 for the part and $120 labor for the repair (total $220, plus sales tax, which they charge on everything here in WV...).

It's been several weeks and so far so good...

Was that price fair? I didn't really have time to shop around, I needed my truck fixed.

yeah...the parts are usually 80-100 bucks for an AC Delco replacement...plus an hours labor to pop it in...so you may have saved 50 bucks if you went to another shop due to labor cost and they got the part 20 bucks cheaper. But another shop may have made you replace the whole encoder motor instead of just the sensor, and thats 200 bucks by its self.

So yeah I'd say you came out good