Service 4WD *FIXED*

[GregBunney]

Hello, trying to chase down a service 4wd message rn. Recently swapped the TC due to it having holes in the casing from rubbing through, then came back home (I do my own work in my hometown and am not living there rn) where I got put into limp mode on my trans, so o took it to a shop because I work crazy hours and didn’t have time or tools to diagnose. The shop swapped out my ignition switch and now I have all my gears again but getting a service 4WD message. Just swapped out the 4wd buttons and it worked fine at first, went to pull out of the garage and it swapped back to 4lo, and died. Got it running again after a second and it’s working fine this start up. Do 03 Yukons need some sort of reprogramming? Did I get a bum switch? Or is the switch not my problem and I should start looking at TC shift motors?

 

[Fless]

I assume this is the AUTO two-speed transfer case? What RPO code, NP8?

You need a good bi-directional scan tool to view the chassis code that is causing the Service 4wd message, and that can give you some good starting direction. Once you have that, codes and diagnostic procedures can be looked up at www.charm.li.

A good scanner will tell you what mode (2wd, AUTO, etc.) is "commanded" vs. "actual." Having said that, the encoder motor seems to be a maintenance item in these, and they're not that difficult to change. No programming needed until you change the TCCM (control module) but I think the Dorman one is not required to be programmed.

If you're handy you could just change the commutator (range position sensor) inside the encoder motor, which is what usually goes bad. You can find YouTube videos on that repair.

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[Fless]

2004 Yukon XL 4x4 Transfer Case Issues

First time poster here. My 2WD, N, 4H, and 4L selector switch doesn't stay in 2WD mode all the time. When I turn off the engine for a short period of time and then restart the motor, the drivetrain selector switch on the dash left of the sterring wheel goes into either the "N" (red light) or 4L...

www.tahoeyukonforum.com

@rockola1971 also has good info on these, you can search for his posts.

 

[Fless]

One question.... when you "went to pull out of the garage and it swapped back to 4lo, and died." Did it actually go into 4lo, or did the dash switch indicate that without it really changing drive modes?

I had intermittent mode indications when my encoder motor went bad, but the actual drive mode didn't change.

 

[rockola1971]

Hello, trying to chase down a service 4wd message rn. Recently swapped the TC due to it having holes in the casing from rubbing through, then came back home (I do my own work in my hometown and am not living there rn) where I got put into limp mode on my trans, so o took it to a shop because I work crazy hours and didn’t have time or tools to diagnose. The shop swapped out my ignition switch and now I have all my gears again but getting a service 4WD message. Just swapped out the 4wd buttons and it worked fine at first, went to pull out of the garage and it swapped back to 4lo, and died. Got it running again after a second and it’s working fine this start up. Do 03 Yukons need some sort of reprogramming? Did I get a bum switch? Or is the switch not my problem and I should start looking at TC shift motors?

When the electrical ignition switch is replaced a PASSLOCK relearn has to be performed. If you were physically in 4LO (You would know if you were) then you have a problem that needs to be diagnosed. If it was just a false indication then it likely was caused by a bad commutator which is located on the TCase Encoder motor. The commutator sends feed feedback to the TCCM so it knows what physical gear the TCase is in after it is commanded to be in a gear. Default is 2wd until you stick one of your boogerhooks on one of those switches on the dash. The commutator is sold and can be replaced separately BUT you must remove the encoder shift motor from the TCase to access it.

 

[Saucy_Walnuts]

I swapped in a rebuilt NP8 in my 03 Yukon with no issues. I didnt need a relearn or anything and also swapped in a new ignition tumbler and ive got no codes other than constantly under "driver 2". I did use the old Encoder although it came with one. Ive had no codes. Is it actually going into 4lo with a audible clunk and lower speeds with gear changes? As stated it could be the commutator which is a simple repair and the part is fairly cheap. But the encoder must be removed from the transfercase to change. It could also be a dirty plug. But a scanner is needed to tell commamd vs actual like stated as well.

 

[houstontaylor]

On my 2003 Tahoe I got the same message and it went away when I replaced the transfer case module underneath the dash. I had previously replaced the switches without any improvement.

 

[waveryd]

In many cases the transfer case encoder ring malfunction does not trigger a dtc. As stated above it is a common failure point and fairly easy and inexpensive to change. Given the symptoms I would start there.

 

[Fless]

I would start by getting the code that's triggering the message, so you're not shooting in the dark.

 

[GregBunney]

Hello, trying to chase down a service 4wd message rn. Recently swapped the TC due to it having holes in the casing from rubbing through, then came back home (I do my own work in my hometown and am not living there rn) where I got put into limp mode on my trans, so o took it to a shop because I work crazy hours and didn’t have time or tools to diagnose. The shop swapped out my ignition switch and now I have all my gears again but getting a service 4WD message. Just swapped out the 4wd buttons and it worked fine at first, went to pull out of the garage and it swapped back to 4lo, and died. Got it running again after a second and it’s working fine this start up. Do 03 Yukons need some sort of reprogramming? Did I get a bum switch? Or is the switch not my problem and I should start looking at TC shift motors?

Thanks for all the input and advice guys! Ended up getting the transfer case buttons swapped out, left it for about a day or two (kept getting the message for service) and now it’s fixed and been solid for about 1 1/2 weeks. I was getting a U1301 code when I scanned them last too.

 

[NoReverseYukon]

I just had this happen. Both the 2WD and the AUTO 4WD lights are on in the dashboard switch. Pushing either doesn't turn them off. Nor does pushing 4HI or 4LO turn those lights on. There is no code under drivetrain, chassis, or body using my Foxwell scanner.

Question - will driving it in this condition cause any damage?
I am operating under the premise that the switch is bad and not the encoder ring.

Thanks.