LMM P0878

LBZ_Baker98

Member
Jul 8, 2016
205
2
18
Texas
Have a buddys LMM that he just bought. Had all kinds of codes being thrown and truck wouldn't move, replaced the TCM and had a it programmed and truck runs and drives now but every few times you put it into reverse it throws a P0878 code and says "range shit inhibited shift to neutral to reset" then it works fine after going to neutral. I was thinking NSBU but wanted a few other peoples opinions since a local shop has already given him the run around. Truck has 225k miles on it and shifts great in the forward gears except this one code and not wanting to go into reverse sometimes. I have used the search feature for this code on this forum but none of the threads had any suggestions or answers really. I don't mess with the internals on these transmissions to much but would like to help him before I haul it 2 1/2 hours to Josh H. since he is the only Allison guy I trust that is even remotely near me! Any help is greatly appreciated.
 

juddski88

Freedom Diesel
Jul 1, 2008
4,503
46
48
Chesterfield, Mass.
Have a buddys LMM that he just bought. Had all kinds of codes being thrown and truck wouldn't move, replaced the TCM and had a it programmed and truck runs and drives now but every few times you put it into reverse it throws a P0878 code and says "range shit inhibited shift to neutral to reset" then it works fine after going to neutral. I was thinking NSBU but wanted a few other peoples opinions since a local shop has already given him the run around. Truck has 225k miles on it and shifts great in the forward gears except this one code and not wanting to go into reverse sometimes. I have used the search feature for this code on this forum but none of the threads had any suggestions or answers really. I don't mess with the internals on these transmissions to much but would like to help him before I haul it 2 1/2 hours to Josh H. since he is the only Allison guy I trust that is even remotely near me! Any help is greatly appreciated.

The above posted chart is useful to get started, but you'll likely need to be comfortable ohming out circuits and checking for shorts with a multimeter to verify the problem.

On another note, you said it is intermittent...does it do it when the trans is both cold and hot, or just one or the other?
 

LBZ_Baker98

Member
Jul 8, 2016
205
2
18
Texas
The above posted chart is useful to get started, but you'll likely need to be comfortable ohming out circuits and checking for shorts with a multimeter to verify the problem.

On another note, you said it is intermittent...does it do it when the trans is both cold and hot, or just one or the other?
Seems to do it all the time for the most part! regardless of hot or cold. It only does it every 30-40 or so times you go to reverse from drive or neutral or park!