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TTG: How I turn off the "Service 4WD" light on the dash in a 2004 GMC?

  
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TTG: How I turn off the "Service 4WD" light on the dash in a 2004 GMC?

 
Truck Trend Truck Trend
Administrator | Posts: 4666 | Joined: 02/07
Posted: 12/29/08
10:22 AM

Q: I own a 2004 GMC Envoy with 35,000 miles and need to know how I turn off the "Service 4WD" light on the dash? I think it's just a service reminder.

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A: In your Envoy's case, it's not that simple. The Service 4WD light isn't a service reminder but an indication from the TCCM (transfer-case control module)--the computer that handles electronic transfer-case operation--that a failure has occurred and a trouble code has been stored in the control module's memory bank. It'll require a technician with a scan tool to proceed with the next step in diagnostics. There are a few somewhat common issues that may turn on your service 4WD indicator. One is the TCCM not waking up when you turn the ignition on--been there, done that. The fix is replacement of the control module and/or reprogramming with the latest/greatest software update. Other faults that may trip the 4WD light and set a code in the control module include a defective wiring harness to the transfer-case speed sensor, poor electrical connections to the module itself, a malfunctioning encoder sensor that signals transfer-case range selection, or a problem with the front drive axle actuator assembly. Had enough? With a little luck, whichever the failure may be, you may come in just under the wire for manufacturer's warranty coverage.  

If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex Steele, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 6420 Wilshire Blvd., Los Angeles, CA 90048, or e-mail us at trucktrend@sourceinterlink.com.

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