Service 4WD light on Silverado pickup


Old 06-09-03, 02:07 PM
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Service 4WD light on Silverado pickup

I have a 1999 Chevy Sliverado 4WD pickup with 75k miles on it. I was driving it and the "Service 4WD" light came on. I was not in 4WD and didn't notice anything unusual while driving it. I drove about another mile and shut it off. I looked for oil leaks and didn't find any. I restarted it and the light did not come on, but after driving about 2 more miles it came back on. I drove a couple more miles and shut it off. I restarted it and the light did not come on again for another 300 miles. I had it in 4WD about 10 days before the light came on the first time to go across a muddy field and it worked perfect then.

So, I tested the 4WD while in the yard. When I was not moving and in neutral, I pushed the 4 High button, nothing happened and the light did not come on. I pushed the 4 Low button and I heard a sound below that I assume was the transfer case switching to 4 Low and the light came on. I pushed the Auto button and heard the same sounds (I assume from shifting back to high range) and that light came on. I pushed 4 High again and the light came on this time. I drove around some and I could tell it was in 4WD by the way it steered when I turned sharp. I switched in and out a few more times and everything seemed to work normally. So, I thought maybe something was just sticking and freed up. But, it came on again a few days ago. After I shut it off it hasn't come on again after driving about 50 miles, but I'm not ready to get my hopes up yet!

Any ideas about what's going on? The manual just says "When SERVICE 4WD appears on your Message Center it indicates that there is a problem with your Automatic Transfer Case. The system is designed to catch many problems before they become catastrophic. When SERVICE 4WD appears you should contact your local Chevrolet dealer immediately." I heard that it could just be a bad switch or something else simple like just needing to disconnect the battery for a minute, so I really don't want to spend a lot of money at the dealer if I don't need to. Thanks.
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Old 06-09-03, 03:06 PM
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Need a scanner to determine the problem in an effective manner. Not DIY repair.

Autozone MAY be able to scan the codes for you.
Old 06-10-03, 01:00 PM
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You probably have a prblem with the switch on the dash-unplug it and plug it back in when service 4wd drive light comes on and doesn't go into 4wd high. After plugged back in should work and light go off. That would be your problem in the switch.
Old 06-10-03, 08:55 PM
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Join Date: Mar 2002
Location: Iowa
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Seen a bunch of this style chassis have problems with the culprit being the encoder motor. That's a fancy name for the thing that makes noise when you push the buttons on the dash. Or in layman's terms, the automatic transfer case shift motor. If this is the case I hope you have a service contract. Last one I did was about $900 installed if I remember correctly.

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