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Author Topic: 2002 Gmc 1000 Allison trans will not shift on 2 times in the last 3 months  (Read 1990 times)


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Need help twice in the last 2months my gmc 2002 Allison trans would not shift out of park


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Hopefully one of our experts will be along to offer suggestions. Meanwhile, check out this discussion on a diesel forum for a possible cause and fix.
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Get your transmission serial number and go to Allison's web site to find out how to pull codes and what they mean.
2008 Newmar Mountain Aire
450 HP ISM Cummins
Allison 4000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-


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Not too sure about the 2002, but my 2004 has an interlock with the brake pedal.  It won't shift out of park unless the brake is pressed.  Your brake switch may need adjusting or replaced.  You could also try the suggestion in post #5 of this thread.
2004 Silverado LB7 D/A CC LB DRW 4x4, Firestone Ride-Rites, Air Lift Compressor, Line-X Bed Liner, Retrax Bed Cover, Backup Cam, Pullrite Super 5th Hitch,  AstroStart 2205A Remote Start
2014 Keystone Outback 5th wheel
Trail-Air Pin Box, Rear View and Side Cams on Trailer,


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  • Posts: 285
is this in a  truck or RV  as we dont know if it could be the auto park system  that is on the drive shaft