Allison 5-speed Fault Codes

[carleaux]

I recently purchased a used truck and discovered a major problem after driving it 140 miles home. I saw a small oil leak in the driveway and this led to me discovering that the transfer case was only held on by one bolt. The tail extension housing on the transmission had cracked around the flange. The rear transmission mount was also broken. As expected, I found that the driveshaft universal joints were in really poor shape.

I ended up replacing the transmission with a used one, which may not have been the best decision, but I did it. I don't know too much about it other than it wasn't having issues when it was pulled and the fluid inside was not in the best shape, a bit brown. The person I got it from is a friend of a friend so I trust that they were upfront with me about the running condition. I replaced both filters and all of the fluid, about 20 quarts of Dex III.

I was planning on rebuilding the transfer case with the Merchant Automotive pump rub kit only to find it was already installed after opening the transfer case.

After the swap the truck has been running fine for about two months. Recently when pulling out of a driveway with a heavier throttle, it hiccuped shifting and locked into first gear. It threw codes P0732, P0843 and P0875. I reset the codes and it drove fine. Since then in about 200 miles of driving it has hung up right after shifting to second and thrown codes P0776 each time. When it does so it locks into first gear.

I found that my front output seal is leaking on the transfer case and I was probably 1/2 quart low so I refilled it. I also took out the output sensor and didn't see anything wrong. I ohm tested it and didn't get a real steady reading, it was jumping around from 500 to 2000 on my meter. I have not checked the two sensors on the transmission.

Any ideas?

 

[carleaux]

Tonight it threw a couple of P0732 codes while in second and limped into third gear. It feels as though possibly there is slipping but I'm not sure.

 

[nwodiesel]

I'm having similar issues as well. Coming to a stop iy stays stuck in second gear almost as a standard trans ac would do if you failed to push the clutch in coming to a stop. Also sometimes ithas a kind of neutral drop leaving from s dead stop. fluid is kinda brown,I can only assume there is an issue. oddly enough I have not thrown any codes. Il post any findings. Cory thanks

 

[830king]

Tonight it threw a couple of P0732 codes while in second and limped into third gear. It feels as though possibly there is slipping but I'm not sure.

The po732 dtc is second gear incorrect ratio...meaning second gear slip most likely. Just a fyi.... po731=1st gear....po733=3rd gear... po734=4th gear.... po735=5th gear

Sent from my SM-G900V using Tapatalk

 

[Mike L.]

It is not often that a trans problem will throw a 732 code. Usually it is a transfer case problem although it could be a blown out apply piston in the C4 clutch.

 

[carleaux]

Mike, what about the fact that I get both P0732 and P0776? Does that make one scenario more likely than the other? The transmission normally shifts pretty smoothly so I'm not sure if I would be able to tell anything about the C4 condition without taking stuff apart.

 

[Mike L.]

776 is a tie up ( in 2 gears at once for a split second ). That might indicate a bad output speed sensor in the transfer case which can cause both of your codes.

 

[bmc1025]

When changing the speed sensor check the wiring harness connected to it. Pull the loom out of the clips on top and look at the wiring thoroughly.

I've had similar issues from the transfercase banging around and nicking the wiring, which later corroded.

 

[Mike L.]

Be a good idea to see if you can move the tone wheel in the transfer case when you have the sensor out. Any movement of the tone wheel will cause your codes.

 

[carleaux]

If the problem was in the transfer case or speed sensor would it be limited to the 1-2 shift as it seems to be so far?

 

[carleaux]

I think it may be the C4 apply piston after reading other posts.

I checked the transfer case sensor and tone wheel and all is good. I swapped the turbine sensor from my old transmission. The problem is still intermittent, usually happens once every 200 miles at this point with fairly light throttles on the 1-2 shift and while in second. When it happens at the shift I get P0776 and it locks in first. When it happens while in second (I think when it's about to shift to third) I get P0732 and it locks in third.

 

[carleaux]

I solved the problem.

I changed the transmission back to the original one with the tail housing from the used one, and fully rebuilt the transfer case. I also changed the NBSU.

Should've thought of this earlier!