Allison 5sp: shift range inhibited

[Lennart]

My truck is throwing the following codes when cold: P0846, P0875, P0700.
Truck will drive forward out of garage initially and reverse but after that I get "shift range inhibited".
Once warmed up no more codes.
Will check for rubbing of cables near the PS pump, any other ideas?

 

[Mike L.]

Could be a bad Pressure Switch Manifold. The switch off a front wheel drive GM 4T40E or 4T45E will work perfect. That should be available at a GM dealer Lennart.

 

[Bako_Dmax]

Ive had a similar code, it was a torn o-ring on the pressure switch manifold. My truck did the same thing.

 

[Lennart]

Finally changed the pressure switch manifold but tranny is not acting any different.
Will loose gear (first or reverse) shortly after driving a few yards. Also re-engages
gear rather harsh sometimes... will only do this when cold, once warmed up shifting is fine.

The ATF was a little colored (still red) but you could not see the pan bottom with more than 1/2" of ATF in the pan. The magnet in the pan had some black stuff on it, nothing dramatic, though.
Will check the ATF level and change the spin-on next and see if that helps. Any other ideas are welcome, though

 

[BALISTIX]

Mine did the same it was the ignition switch in the column it wasnt sendind enough voltage to the TCM

 

[Iceman56]

Check you ATF level first thing, mine was doing this and just low on fluid

 

[Dudgy]

Mine did exactly that and it was my NSBU switch, i bet yours is on its way out too