"Service 4WD" Light

[floydpink]

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 4 LO doesn't seem to work; the light on the button just flashes.

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.

[RyanbabZ71]

sounds like you need a new switch which isnt expensive and it should be easy to fix yourself.

 

How come you havent ever put it in 4wd? I try to put mine in at least once a month to keep it fresh.

 

My mom rarely put her blazer in 4wd and had a problem with the 4wd system.

[AZ-Z71]

It is the push button module that is more than likely bad. I replaced mine and a coworkers. Both trucks were 99 as well. Mine did exactly as you did. The part is at the dealer for about 30 to 40 dollars. Cheaper on line. Sould only take you about ten minutes of your time to install.

 

If your 300 mile trip is involving using 4 wheel drive then sorry to say you need to run to the dealer tonight to get the part. If not then there will be no problem. You just won't be able to use 4 wheel drive.

[silverado man]

I had the same with mine the lights blinked but 4wd still worked for me. I would say your problem is the switch. The part # is 15709327 if you click <--- on one of our preffered vendors you can find it cheaper than your local stealer. I wouldn't think you will have a problem with it, when I had the problem I drove on it for like 4 or 5 months before I replaced it. Been working great since (about 8 months).

 

FYI you to get your T-case into 4-lo you have to be moving but less than 5mph(I believe is the speed).

[seadoons]

Doesn't the truck also have to be in neutral to get it into 4L?

[AZ-Z71]

Yeah I always found this to be tricky. You have to be moving under 5 miles and hour and need to be in neutral. Seems like you can't do both. Usually I get the truck moving a little in drive then shift into N and then set it to 4 high then 4 lo. Usually goes right in without a problem.

[floydpink]

Yep, I went out and popped it into neutral and that seemed to do the trick with 4 LO. (I guess I should have read the manual more carefully.)

Thanks for the advice on how to fix the problem. I guess I'll just have to deal with the light as soon as I get back tomorrow.

[Z71Adrenaline]

Sorry to argue, but the truck doesn't HAVE to be moving to get into 4LO. We have a 2000 and a 2001 and we just put the truck in neutral before moving and select 4LO. Works like a charm everytime. In fact, I did it this morning.

[cowboy02]

As for your light problem I find it hard to believe that there would be a Idiot light comming on for something like a bad switch in the dash... Sounds like you could have more problems then switching into 4X4

[AZ-Z71]

It is a common problem and when you call a service tech they automatically tell you it is the switch. I guess they have seen enough of them. Believe it or not it tells you "service 4 wheel drive". Probably some sort of little diode goes bad in the switch and the computer picks up a bad signal. No real harm driving with it bad except you might not be able to use 4 wheel drive when you need it, and the d**n light is on in the dash which is an annoyance.