Question about 1999 Chevrolet Silverado 1500

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Service 4wd light on

My "Service 4WD" light, on my 1999 Z71 Ext Cab, is on and I am having trouble getting it to go in and out of 4wd. Any suggestions?

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On most cars, there is a vacuum operated actuator that shift tranny into 4x4. Sometimes this actuator can get faulty or the circuit to it can get faulty. Other types have just the circuit operation which can become faulty. It should be placed on a diagnostic machine to determine if the system is faulty or if it is just a bad switch.

Posted on Sep 09, 2009

  • Mike Abrams
    Mike Abrams May 23, 2012

    Had a problem with my 99 Silverado Z71 shifting into Auto 4WD for the first time after 225000 miles and the Service 4WD came on...turned key off and everything went back to normal again. tried placing in Auto 4WD again and the thing hung between 4wd & 2WD, both lights on; Auto 4WD and 2WD...turning the key off would not reset problem this time, Solution to get it back to 2WD; I turned key switch to the ON position, opened the hood and pulled the ATC fuse out... the actuator activated, and I said hum...this may i plugged the fuse in again and heard the actuator moving again, cool, so I did this a couple of times. I got back in my truck and turned the key switch to off and then back to run... now the indicator light was showing it was in 4WD HI. Hit the 2WD button and it went back to 2WD w/ no service 4WD light... temporary fix but at least I can drive it until I find the actual cause of the auto 4WD failure.



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