2005 Gmc Sierra Z71 "service 4wd" Message

rjbaiad · October 19, 2010

Hi guys,

I have a 2005 GMC Sierra Z71 with a 5.3L engine and recently started having some issues with the 4 wheel drive. Several weeks ago one day I noticed my transmission in my truck was doing some really strange things. As I would accelerate I noticed the truck would start jerking. It felt like the transmission was downshifting and upshifting really quick. Once I got past about 45 mph the problem would go away, but only seemed to happen when I was accelerating. Later that day the problem stopped buy my check engine light came on, so I stopped by O'Reilly's and had them put a diagnostic computer on the vehicle and the fellow that helped me that my particular model of vehicle had an issue with some sort of sensor on the 4wd that would occassionally cause my truck to act like I was describing above. He said that sometimes hitting a hard bump may cause this sensor to do strange things. He told me that he reset the check engine light and once it was reset, it should be fine. Truth is, after that everything was fine.

Yesterday I was leaving my sister's house, and noticed that the lights on the panel had switched from an amber light on the 2wd to a red light on the N and my truck I got a message that said "Service 4WD." I tried switching it to 4w hi and the amber light would just blink for a few seconds then go back off without changing anything. I also tried this on 2wd with the same result. I then got home and put it into neutral and tried putting it into 4 lo and nothing happened. The light blinked just as the others did then turned off. I then turned off the truck for a few seconds and restarted it hoping the problem would clear up, but it didn't. The lights turned on and flashed like they normally do when you start the vehicle, then they all turned off and never came back on. I tried shifting it to 4 hi and 4 lo and nothing happened but I would still get the service 4wd message. I borrowed a friends diagnostic computer today and when I got home it said there was nothing wrong. I did some research on the internet to find that the switch could be bad, so I pulled out the panel and pulled both plugs on the switch and as far I could see, there was nothing wrong. There were no broken pins or frayed wires that I could tell.

I then put it all back together and started the truck once again and still had the same problems. Lights would flash when I would start the vehicle and then they would all go off and I would again receive the service 4wd message. I tried plugging in the computer with the key off and obviously it couldn't communicate. So I started the vehicle again and although I got the service 4wd message, it still said there were no problems. Once again I turned off the key and turned it back on and now everything works fine. I was able to shift it from 2wd to 4 lo and 4 hi with no issues and am no longer receiving the service message. Could this still be the switch or could this be a bigger issue?

gmtech4 · October 20, 2010

what was the GD code ???

rjbaiad · October 20, 2010

It didn't have anything. It said that all tests passed. If you are referring to the code at O'Reilly's, I don't remember what it was. That was several weeks ago. I thought it was a glitch that I never would see again.

Thanks,

Ryan

what was the GD code ???

gmtech4 · October 21, 2010

we need a code ,do NOT throw parts at it ,ok?

RJNehus · April 25, 2011

Hi guys,

I have a 2005 GMC Sierra Z71 with a 5.3L engine and recently started having some issues with the 4 wheel drive. Several weeks ago one day I noticed my transmission in my truck was doing some really strange things. As I would accelerate I noticed the truck would start jerking. It felt like the transmission was downshifting and upshifting really quick. Once I got past about 45 mph the problem would go away, but only seemed to happen when I was accelerating. Later that day the problem stopped buy my check engine light came on, so I stopped by O'Reilly's and had them put a diagnostic computer on the vehicle and the fellow that helped me that my particular model of vehicle had an issue with some sort of sensor on the 4wd that would occassionally cause my truck to act like I was describing above. He said that sometimes hitting a hard bump may cause this sensor to do strange things. He told me that he reset the check engine light and once it was reset, it should be fine. Truth is, after that everything was fine.

Yesterday I was leaving my sister's house, and noticed that the lights on the panel had switched from an amber light on the 2wd to a red light on the N and my truck I got a message that said "Service 4WD." I tried switching it to 4w hi and the amber light would just blink for a few seconds then go back off without changing anything. I also tried this on 2wd with the same result. I then got home and put it into neutral and tried putting it into 4 lo and nothing happened. The light blinked just as the others did then turned off. I then turned off the truck for a few seconds and restarted it hoping the problem would clear up, but it didn't. The lights turned on and flashed like they normally do when you start the vehicle, then they all turned off and never came back on. I tried shifting it to 4 hi and 4 lo and nothing happened but I would still get the service 4wd message. I borrowed a friends diagnostic computer today and when I got home it said there was nothing wrong. I did some research on the internet to find that the switch could be bad, so I pulled out the panel and pulled both plugs on the switch and as far I could see, there was nothing wrong. There were no broken pins or frayed wires that I could tell.

I then put it all back together and started the truck once again and still had the same problems. Lights would flash when I would start the vehicle and then they would all go off and I would again receive the service 4wd message. I tried plugging in the computer with the key off and obviously it couldn't communicate. So I started the vehicle again and although I got the service 4wd message, it still said there were no problems. Once again I turned off the key and turned it back on and now everything works fine. I was able to shift it from 2wd to 4 lo and 4 hi with no issues and am no longer receiving the service message. Could this still be the switch or could this be a bigger issue?

Ryan,

What ended up being the problem? I just had the same scenario happen to me last week, except the "service 4wd" came on right after i turned on OnStar??

thanks

Troy31 · April 25, 2011

My '04 had done the same within a couple weeks after I got it I believe, maybe longer. I started it, let it run for a bit then got in and noticed the same thing with the lights for the 4wd and the Service 4wd message... I tried changing it to 4hi, etc. no go. Just stayed in 2wd.

Anyway, I had shut the truck off at my next destination, went in, came back out and the message was gone and everything worked normal again. A while after that I had all the fluids changed in the diffs and the T-case. Regardless I have not had a problem since!