4wd not engaging


Old 04-11-04, 06:39 PM
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Join Date: Nov 2002
Location: Canada
Posts: 105
4wd not engaging

1999 GMC Envoy 4.3L 4wd auto.Its push button to engage drive modes. It only works on 2wd Hi and 4wd Lo but will not engage 4WD Auto or 4Wd Hi. Any Ideas?
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Old 04-12-04, 12:37 AM
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I've yet to see one of those automatic locking 4wd units NOT seize up. You're probably better off converting it over to manual locks. But I'm sure one of the resident experts here will have a way to fix your problem. Good Luck
Old 04-12-04, 04:33 AM
carguyinva's Avatar
Join Date: Nov 2003
Location: Shenandoah Valley
Posts: 1,147
you can't convert to manual...

...locking hubs. take it to a competent tech and have it scanned for codes. it may have a bad encoder motor...it may just need to be exercised. sometimes they freeze up due to lack of use. good luck...
Old 04-12-04, 04:39 AM
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
You need to have atc codes checked to accurately diagnose it but I would suspect the mode switch is faulty(dash select switch).I think you may find a mode switch malfuntion code stored,if so replace the switch and clear the code.B2725 is the code # for the mode switch.

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