"Service 4WD" Light Problem

I own a 1999 GMC Sierra Z71 that I never put in 4WD. About a month ago, a few minutes after starting the engine, the "Service 4WD" light came on. After restarting the truck, the light did not come on so I thought nothing of it. About a week later, it did exactly the same thing, so I restarted it again. It has not come on again until today; a few minutes after starting the engine, the light comes on and this time restarting does no good. I tried putting it into each of the 4WD settings, and found that all of them work.
I was planning on taking a 300 mile trip tomorrow in the truck...should I cancel on account of the problem?
Any ideas on what the problem is and what it might cost to fix?
Thanks.

The Service 4wd indicator illuminates when there is a problem with the 4wd system (its the "check engine light" for your 4wd system)
There will be a diagnostic trouble code stored
Most likely scenerio...the module is bad (thats the switch on the dash) but have it diagnosed before throwing a part at it
As far as your trip.........shouldn't be a problem.

Mr. FloydPink,
You stated that you never use your 4 wheel drive on your truck. The problem is, in order for the parts to be properly lubricated, you must use it occasionally. Try running it around for a bit in all ranges and the problem should disappear. What happens is that the sensors inside the t-case show that no lubricant is present and just needs a cycle of use to read correctly. Try that before any dealer or shop...just my $.02 Hope it helps!

My 99 did the same thing and the switch was bad. They replaced it in no time and it plus labor was only $65.

I just had this problem on my 2003 Suburban. There is a new fix and the problem was corrected in 30 minutes. The problem was with the computer program.

I own a 1999 GMC Sierra Z71 that I never put in 4WD. About a month ago, a few minutes after starting the engine, the "Service 4WD" light came on. After restarting the truck, the light did not come on so I thought nothing of it. About a week later, it did exactly the same thing, so I restarted it again. It has not come on again until today; a few minutes after starting the engine, the light comes on and this time restarting does no good. I tried putting it into each of the 4WD settings, and found that all of them work.
I was planning on taking a 300 mile trip tomorrow in the truck...should I cancel on account of the problem?
Any ideas on what the problem is and what it might cost to fix?
Thanks.

I had the same problem on my 200 Sierra. It was fixed under warranty and I believe it was a switch that tells the light to come on.

The way mine was fixed was by changing the computer program with a new update. The service tech said that the update had just been published and prior to this month they had been chaning the switch when this problem occurred. As it turned out, the problem was in the program.

I had the same problem on my 200 Sierra. It was fixed under warranty and I believe it was a switch that tells the light to come on.

Here is a good link for this problem
http://mct.truckmoxie.com/forums/topic.ten?pos=3&id=60504&q=Service+4wd.

I changed my switch 3 months ago and problem was fixed.

The Service 4wd indicator illuminates when there is a problem with the 4wd system (its the "check engine light" for your 4wd system)
There will be a diagnostic trouble code stored
Most likely scenerio...the module is bad (thats the switch on the dash) but have it diagnosed before throwing a part at it
As far as your trip.........shouldn't be a problem.
My service 4WD light is on, and the Auto 4WD light and 2 HI light are on. Valvoline Quik lube place says when they pulled plug to drain the front diff, there was Dex in the diff along with the other fluid. Filled it and told me to go to the dealer for service; Didn't charge me. I am concerned.... can trans. fluid get into the diff??? Seems to be running fine; but what are all the lights about???

I am really freaking about my 1999 GMC z71 ext. cab truck. I LOVE this truck; 82,000 miles, but new to me. The Auto 4WD light, the 2HI light AND the SERVICE 4WD light are all on!!! Seems to be running fine. Slow leak from front diff (I think)....
Really don't want the expense of a dealer service call. Any ideas? Recommended repair shop, i.e., full service garage vs. trans shop??

After reading this and other forums on this subject, I too have experienced the problem with my 2001 Silverado Z71 truck. It's symtoms included the switch 2WD indicator going off and on periodicly and the "Service 4WD" light coming on and going off periodicly. If I tapped real hard on the dash area around the switch, this would cause the switch indicators to go off and on as well. When I first purchased the truck, some 60,000 miles ago, all switch indicators would flash on each time when the ignition switch was turned on, then the selected drive indicator would remain on. Ever since the truck turned 45,000 miles my problems began. I went to the Chevrolet Dealer and asked if there was any TSB's on this problem and they said they recognize there is a problem but there are no recalls. Most forums I have read to date point to a defective "Transfer Case Control Switch". This has been a nuisance to me more than anything else see this light popping on and off all the time. So I finally broke down and went to the dealer to get a new switch that they now use in place of the ones with this problem. It took 20 minutes to install. All the normal indications returned and so far,the truck is back to the way it is suppose to be. The switch costs $60 with tax at the dealer. Make sure you have your VIN ready when you talk to the parts desk.

Happy Trails

my 99 had the same problem and had gotten the switch replaced like madmalibu did, that fixed the problem, and like jasonaspears said you should use your 4wd at least once every couple of weeks or so to get things moving in there and keep it lubricated.

Ditto for my 2000 Sierra. Service 4WD, blinking indicator lights, and the all the related hoo hah. I just popped off the front of the dash, and changed the switch. Takes 10 minutes tops.

I experienced the "Service 4WD" error light on my 1999 GMC occasionally for the passed 6 months. Switching in and out of 4WD seemed to clear the problem for awhile. Lately, it came on every time I used the truck so I took it to the dealer. The cause was traced to a failing 4WD Switch (error code B2725). The dealers charge for the switch was $87.38. The switch FP # is 19168767, description Switch 4.563. Labor cost with diagnosis was $163.51 for a total of about $250. Note: Complain to the service manager if "environmental charge/supplies" is added to your bill. Hope this info is useful to someone.

I Have a 2000 GMC Sierra 2500 EXT Cab and it rained pretty bad then the next day i got in my truck started it up and saw the Service 4WD Light came on :runaround: so i shut it off and turned it back on light went away went out for the night got back in the truck light came back on i tried everything looking to see if it was a loose wire or something and i do use my 4WD once in a while....So can it be that one of the solenoids or a sensor shorted out cause i have a 24hr drive coming up soon and i would like this fixed any input would be nice thanks

I had the same problem with my 2000 Suburban. Check the connector for the encoder motor on the transfer case. Mine had a broken clasp so I cleaned it, put on some di-electric grease, zipped tied the connector back together and problem solved. I hope it is that simple for you guys as well!!

About 6 month ago, after driving my 2001 chevy blazer about 2 miles my 4WD felt like it shifted down to a lower range, Of course I panicked because the traffic was pretty heavy..When I was able, I pulled over,Got out my book from the glove box, I was pretty nervious
everything just blured over,I couldn't find out what to do.
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I called a friend and he said to ."put it in netural and hold the Top Button down for 30 seconds.'
It worked..Now this morning after my wife pulled out from our drive ,I heard a clunk and it did the same thing.So she put it in netural and held the top button down for 30 seconds..
It worked.
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Any idea what's wrong?..I checked the fluid level .But my eyes are bad and can't tell if it was low..
Could low fluid cause this problem.??
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My wife just now told me the "Service 4WD Light"started to come and on and off last week
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Please Help..
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Hi all,
Service 4x4 ligth comes up on my Yukon 2005. Its been flashing for few months. Now, ramdomly car shift to 4x4 by itself while driving. I'm unable to control the transmision mode pushing on the panel 2wd, 4-lo, 4-hi switches. I have been searching and reading coments about this issue. Cause of problem are many. So far, the ultimate solution I found is to go the dealership for a computer software update before replacing any part and go from there. The new software should give you the right code of what is wrong.
Possible problems are: Low transfer case fluid or insuficient lubrication due to lack of use of 4x4, the panel switch itself, the 4x4 tranfer case relay, 4x4 control motor in front axel, wiring, or encoder sensor (c0327 code).
My research shows that these repairs cost about $800.
If not repaired soon, car could engage in 4x4, and a turn on pavement could damage gears and other parts. That happends to a someone I know with a Chevy Z71 pick-up truck 2003 and the repairs were $2300.!!!
Good luck

I have the same results as above but either none of the lights light up or they all do. Either way it doesn't engage no matter what you select. 99 Silverado 1500. Thoughts? It won't randomly try to engage while I'm driving down the highway will it?