Service 4WD Light

RichZ · May 24, 2014

I have a 2001 GMC Sierra half ton pick up. The "service 4WD" light goes on occasionally, and at the same time the ABS light went on. I took it to the garage that I've used for 13 years, with excellent results in the past. They said nothing about the 4 WD came up on the computer, but both front bearings were bad, and that's what was causing the ABS light. They thought the bearings might also be causing the "service 4WD" light, as well. They replaced the bearings a week ago, and all was well, until today, the "service 4WD" light came on again for about 1/2 hour and then went out. I should add that throughout this, the 4WD works flawlessly. Has anyone else had a similar problem? Does anyone have any idea what is going on with my truck?

Thanks!!!!!

aczlan · May 25, 2014

Looks like the switch assembly in the dash and the motor in the tcase are frequent culprits (per: Four wheel drive problem 2000 gmc sierra ).
I would order a new switch ($35-60ish depending on the supplier) and see if that fixes it.

Aaron Z

RichZ · May 25, 2014

WOW!!! Thanks!!!! I'll try that.

Gunny · May 25, 2014

I've read on some other forums about the same issue. Some have said that if the electrical connectors on the transfer case and actuator get loose or corroded, it will throw the service 4WD code. Easy and cheap to check them out. I pulled mine, checked them and added some dielectric grease just to safe the last I was under the truck.

Others have said that if fluid levels get low enough in the transfer case or the front differential that it doesn't splash up on the sensors, it does the same thing. Another cheap and easy check, unless you have the 4WD controls on the dash, then you need the expensive Auto Trak II fluid for the transfer case, but if it is low, then a $10 bottle of fluid is still a cheap fix.

I'd check these first then if the problem sticks around, replace the dash switch first, then the actuator.

HHR · May 25, 2014

The first thing I would do is pop out the 4WD switch and re-solder the connections inside. there are about 12 that are common to crack. Takes about 15 minutes and costs you nothing.

ericb2400 · May 25, 2014

My 03 taho does the same thing. It also seems to have a mind of its own. Goes into 4wd or 4 auto when started on its own. Sometimes the lights indicate that the t case is in neutral but it still goes 8-/. When it does that I pull over and stop, put the tranny in nutral and hit the 2wd button. Seems to work.

Do youall think it may still be the selector buttons?

Sent from my iPhone using TractorByNet

HHR · May 25, 2014

ericb2400 said:
My 03 taho does the same thing. It also seems to have a mind of its own. Goes into 4wd or 4 auto when started on its own. Sometimes the lights indicate that the t case is in neutral but it still goes 8-/. When it does that I pull over and stop, put the tranny in nutral and hit the 2wd button. Seems to work. Do youall think it may still be the selector buttons? Sent from my iPhone using TractorByNet

Pull your switch out and inspect the solder joints. My cousin's truck was not shifting into 4-Low or 4-high and re-soldering the switch fixed it.