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Service 4 WD light is on

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Based on the following info from my service tech CD's, I pulled a fuse under the hood, waited 30 seconds, put it back in, and the message went away when I cranked the truck again. Hasn't come back, and that was six weeks ago. Apparently, if the problem is recurrent, you have to go on and have that reprogramming done (described below).


Or, it could be the switch failing, like everyone agrees is very common.


Adm Msg - Inoperative 4WD/AWD or Service 4WD Indicator (Admin Number VSS20020131 10/4/02) #VSS20020131 - (Oct 4, 2002)

Adm Msg -- Inoperative 4WD/AWD or Service 4WD Indicator (Admin Number VSS20020131 -- 10/04/02)

Chevrolet Silverado, Tahoe, Suburban, Avalanche, TrailBlazer, TrailBlazer EXT; GMC Sierra, Yukon, Yukon XL, Envoy, Envoy XL; Oldsmobile Bravada


With RPO Codes: NP8 - Autotrack Transfer Case; NP4 - Autotrack Transfer Case; NP1 - Electric Shift Transfer Case




Corporate Bulletin Number 02-04-21-006A will supersede this message.



Customer Concern

Some customers may comment that the service 4WD indicator is on, or the 4WD system is inoperative.



The Transfer Case Control Module (TCCM) has not received the wake-up call during key-up and has remained in the "sleep mode." When the TCCM is in the "sleep mode," it will not communicate with the class II bus or the Tech 2.



Remove the underhood TCCM fuse (labeled ATCM or TREC). Wait 30 seconds and then reinstall the fuse. The module should "wake up" and communicate with the Tech 2. Reprogram the TCCM using normal SPS procedures, using operating system calibration number 12580062 (or the most current calibration).

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