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Allison Transmission Limp mode.

Yahoo Message Number: 16010
On our way back from AZ this spring I had transmission go into Limp Mode. Whenever downshifting from Overdrive to 4th gear. Transmission would stay in 4th gear with torque converter unlocked. This kept engine running at 3000 rpms for 62 mph. This also turned on the service transmission light under radio. To reset I pulled off road. Turned engine off counted to 10 and restarted. All was OK until engine needed to downshift from overdrive to 4th gear. Then stop again and reset. I found that if I used OD switch in dash to downshift trans did not go into Limp Mode. Made it home with no other problems.
Took motorhome to local diesel mechanic. He pulled pan to check for any crud in trans oil. Found nothing. I replace trans oil last fall. Replaced A solenoid and wiring harness. They took it out for road test. Same problems as I had. They cleared all the codes thinking I would get new codes on way to Allison. Code was P0735. Something to do with 4th 5th gear clutches.
I took it to local Allison dealer thinking I may need a rebuilt trans. Allison ran all their test and checked all wiring connection and plugs that connect transmission control module to transmission and engine control module. Found no problems. They could not get limp mode to happen or get a fault code during 2 road test.
I picked up motorhome the next day. Took it out on the road and tested it same diesel mechanic and I had done before. Could not get it to go into limp mode. In fact it would not downshift in the same places where it had faulted before. It accelerated instead of downshifting. Little confused about this. Because it always down shifted in this situation before.
Talked to Allison Tech. He explained what he did to check trans out. Their connection lets them check all operation of the transmission. His thinking was that one of the connections that he check may have not been seated properly. Plus I believe the procedure he does ends up with a transmission relearn.
Buyer of my motorhome is aware of the problem. It is running good for him. I did not sell motorhome because of this problem.
I may have saved a few dollars if I had gone to Allison first. Maybe? Between the 2 places I spent under $700. Allison's diagnotic was $260. Included 3 hours of labor.
Hope this info helps someone else.
Best
Ron Hall