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service light on 2004 GMC Sierra 2500 HD

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my 4wd service light came on this morning but is now off could you tell me why?
(3) Answers
We just added this article last week, hopefully it will help you with your 4wd issue: http://repairpal.com/gm-4wd-warning-light-issues
The service 4wd light is like a "check engine" light for your 4wd system. When the light comes on a fault code will be set in the transfer case control module. This fault code can be read with a scan tool. The stored codes should help isolate the portion of the 4wd system that is causing the fault.
I had the same issue. There is a sensor located on the front diff. I disconnected and cleaned the connection. Quick fix...