Intermittent SERVICE 4WD Message

[MassHoe04]

That sounds like a button or Tcase module problem. Doesnt fit the symptoms of the dirty commutator ring in the shift motor that is stereotypical.

Everything came back to normal last night... I think I'll hold off on doing anything further or getting any parts until something happens again.

 

[rockola1971]

Everything came back to normal last night... I think I'll hold off on doing anything further or getting any parts until something happens again.

Run all the switches (4hi, 4lo, auto4wd, 2wd) all through the positions. Exercise it which will clean the the commutator ring down in the shift motor. Do this for 5 or 10 mins. If the original problem doesnt come back then the dirty commutator rings was the problem. Not likely to be the Tcase control module. Electronics dont usually heal themselves unless of course its corroded wiring harness connector to module.

 

[BoatyMcBoatface]

i would also check the front axle electrical connection. that connection gets loaded with road crap and is prone to failure. I took all connectors off and sprayed with dielectric spray. I live in an area that seems like salt is of no value and they throw it on the road even in the rain.

 

[George B]

I would put money on the dash switch. I had a 03 Sub with the same issue. I found bad solder joints for one of the plugs on the board. This is what I followed to repair it. https://www.gmfullsize.com/threads/99-sierra-service-4wd-switch-repair-how-to.40730/

 

[MassHoe04]

It has been almost 2 weeks and this has not returned as of yet. I have been clicking the selector buttons every once in a while to have it shift from 2H-4H-Auto and back to 2H.
I do it when I think of it over the last two weeks and seems fine so far. Could very well be the dirty commutator as previously suggested... If the issue returns, I let you all know and break out the Tech 2 to see what is going on. But, for now... All is good in the hood.

 

[Eric Pylant]

I apologize if this was said already, but google “encoder ring” for the Tahoe. This will cause intermittent illumination of the incorrect 4x4 setting, no light at all, and the intermittent service 4x4 light. Then some times it will work fine.
If all else fails, this is a really easy and cheap fix. There are good YouTube videos on it too.

 

[Fless]

I apologize if this was said already, but google “encoder ring” for the Tahoe. This will cause intermittent illumination of the incorrect 4x4 setting, no light at all, and the intermittent service 4x4 light. Then some times it will work fine.
If all else fails, this is a really easy and cheap fix. There are good YouTube videos on it too.

That's what he's calling the commutator. Same thing (and a good suggestion).

 

[MassHoe04]

On mine, it has been 6 weeks since last DIC message to "Service 4WD".
So far, several occasions to exercise and engage the different modes and no return of the message to date.
I suspect the PO rarely engaged 4WD.

If it ever returns, I'll post if something gets replaced.
For now, I will continue to exercise and engage the system at least once a month and pretend nothing happened.