Allison p0763

[buellxb]

Hi guys,
I am having a problem with my truck,it keeps getting stuck in one gear it will not shift in to the next gear or down shift. The code I keep getting is p0763 and I get a message saying Range shift Inhibited. I just put on a new NSBU switch but did not help. Thanks for any help you can give me.

[buellxb]

Hi,
Sorry I did not put the rear truck I have. It is a 2004 LB7. Thanks for any help you guys can give I sure need it right now.

[Kennedy]

Is this something that just happened out of the blue?

Here is what the description is:

Shift Solenoid (SS) 3 Control Circuit High
Voltage


I'm admittedly a bit weak on my Allison electrical. Sounds like a solenoid issue, but just for grins I would unplug and reseat the large connector going into the trans.

[buellxb]

Yes it just stared doing a week ago I could clear it and you could go for a day or so now it just keeps coming on right away. I will try the big plug. Thanks

[THEFERMANATOR]

P0763 is for the E shift valve solonoid. This code indicates that there is a problem in the resistance that the TCM is measuring in the solonoid itself. Does it trip when you start it or only after a 3-4 shift? If there is actually a solonoid problem I would expect it to trip right away. Unplug the trans plug(round one on passenger side rear of trans) and inspect for corrosion or trans fluid. Next drop the pan and inspect the harness. Also check teh wiring harness up by the power steering pump as this is a known spot for frays. Check the resistance of the E solonoid(center one in the lower portion of the valve body), it should be at 20-30 ohms at 72(ALLISON specs 22 ohms cold). Also you could try swapping the E and D(the D is the solonoid right next to it that is the same size, and both of them can be swapped without disassembly other than dropping the pan) shift solonoids and see if it throws a different code. It seems that LLY's have a known issue of the wiring from teh TCM to the trans shorting out when I did a search on this.

[almondfarmer]

WOW, Thanks for the thread. Just having a problem with my '02 D-Max. Stalled very suddenly. The shop found a frayed wire and sent me on my way. Cheap fix and ran great... for only 100miles, then a transmission "limp mode" and wouldn't start again. Now it's at another shop. They cleared the code and said it magically started. The tranny checked out fine. However, it threw another code - a different one (I don't know which this time, but the first was for "excessive pressure"). They reset and trouble-shooted the problem. The transmission checked out "OK". Since the pickup is 100 miles from home, I'm going to pick it up Tuesday.

From the post, it appears the problem is the older wiring harness being cracked and touching something on the housing. Would this make sense for the transmission problems as well?

[Inspector]

I had this same problem with a 2003 lb7 and ally. It turned out to be the ignition switch. The tcm was looseinng the required voltage it needed and therefore went to "shift range inhibited". I have heard of a few with this problem fixed with switch replacement.
Denny