Allison transmission code 55-17 - Solved

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Herriman UTAH
My business partner's wife wanted to drive the 7 Ton and so I let her take it for a spin when she was in town. BUT we did not wait for the warm up time and the tranny was cold. The outside temperature was below freezing. She drove about 50 feet, then she wanted to back up so pushed reverse, and then we got the transmission check light. At that point the tranny went to N and the truck would not move. We tried everything and the tranny would not shift to D or R. So we were stuck. The video is on youtube if you want to see it. I had a nightmare about spending $5,000 for tranny and then $2,000 to have someone install it.

Anyway, I figured out later that it was due to driving with a cold tranny and it is known issue and expected to do that. It throws a code 55-17 on the Allison transmission.

So I googled it and did not find a lot of information that made sense until I found a military vehicle operators manual.

It said that the code was possible when driving a truck with an Allison automatic transmission, shifting from D to R, if the transmission was cold, and if the tranny was NOT using Dexron fluid. Well, all that fit our situation.

So the answer is to:
  • Let the tranny warm up before driving (the book said above 50 degrees F)
  • If you have to drive it cold, do not go from D directly to R. When changing direction, go to neutral first, wait a couple of seconds, then press the other selection.
It notes that this could also be caused by low fluid levels.

So it your Trans Check light comes on don’t panic, check the temperature, check the fluid level, and then panic.

Another thing I found out is you do not need the expensive Cat ET software to figure out the codes. Now MAdams has an unlimited budget but if you don’t have an unlimited budget then pull off the cover to the glovebox and hook up the wires to the self diagnostic screen. Once you do that you can go through the menu and find the codes. Now I thought the code was all it showed but actually, it was giving me a hint as to what the problem was, I just didn’t know it. So I then started to google the code. I was lucky that I found what my problem was.

BUT, if you have the code, google is not helping, and you don’t know what to do, then there is a web site that can help. Go to and sign up for a free account. Then you enter your engine/transmission details and type in the code. The web site then tells you what the problem is. If you pay some money to upgrade your membership then it will also tell you how to fix it.

So I used truckfaultcodes and entered my code. It then gave me an English description of the issue. It looked really familiar so I looked at what the truck told me below the code. It was an abbreviated version of the same thing. So if I had spoke the right language (truck language), I would some idea what was going on just by reading the 4 line screen in the truck.


The 55-17 is the code. Then it tells you that it happened a while ago and it is not happening right now (INACTIVE). Then it tells you how many times it happened. I don't know why there isn't a 1 there. The last two lines are the abbreviated text description of the code. What the text means is "C3 clutch is the oncoming clutch in a shift and the C3 pressure switch did not close at the end of the shift. Operator was shifting from 1st gear to reverse." So it is possible to figure out some codes without hooking up a computer to the truck.


San Dimas, CA
The TM calls for 15/40 diesel oil. Jon, I'm the one with unlimited budget? Says the guy who just bought his 2nd 7 ton lol. Mr money bags

Sent from my SM-G975U using Tapatalk
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