04.5 Allison problem

Stephenj3

New member
Oct 18, 2019
7
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Canada
Hi all, first post so forgive me for any mistakes! So a few days ago, my transmission suddenly stopped registering in park. The line under P wouldnt come on and the truck acts as if its in gear (doors wont auto lock/unlock door chimes when doors are open). I got under there and sure enough the cable and NSBU I think its called were looking fine. I had someone move the lever into all positions and the switch on the side of the transmission responded accordingly.

And as of today it wont register in P R or D. Only in N 3 2 1.
It does however work fine, all 5 gears work and so does drive and reverse, it just doesn't register or show the lines under the gear selected other than N 3 2 1. My CEL came on and the SHIFT RANGE INHIBITED message pops up occasionally while flashing under 3. Where do I start with diagnosing this? I dont have a code reader on hand and will probably head to a trans shop after some feedback. Its a 2004 LLY. Thanks!!