intermitent problem on 5 speed alison

jacques nolin

New member
Jan 8, 2024
17
6
3
st philippe quebec canada
used the truck today all went well until i got home put in reverse no go flashing r light put it in drive no go same in other gears waited 10 minutes back to normal it thing i need to check carefully the wiring harness and the male plug at the rear as you suggest thank for your input will keep you up to date as soon as i am able havea nice day .
 

Bdsankey

Vendor
Vendor/Sponsor
Feb 1, 2018
4,224
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Larsen, Wisconsin
Every time that has happened to me/my customers a genuine Allison/GM NSBU fixed it. I've seen them get damaged during installation as well. My new parts store brand NSBU (I was out of GM/Allison at the time) failed within 2 months. They warrantied it and it is now an emergency backup at the shop incase we ever run out of GM/Allison again haha.

Since the NSBU directly controls what gear is displayed AND it is external to the trans I doubt your issue is inside the pan. I would still check the passthrough connector for fluid.