http://www.dieselplace.com/forum/smileys/Confused.gif Last weekend while returning from a fishing trip I was in the a construction zone in the mountains and the SES light came on. At first everything seemed normal but as I was able to speed up it appeared the Allison would not go into OD. Tow-Haul and OD lockout worked fine. Finally got onto level ground and it would go into OD. Got home and made an appointment with the Stealer - SES light still on. On the way to the Stealer (two days later & after about 15 start cycles) the light went out.


Dealer found a P0733 code in the history from 40 start cycles ago. They reset the code, performed clutch test, checked line pressure and did a road test. All is OK.


3 Questions?


1. What does the P0733 code indicate?


2. What could cause the code?


3. Should I have any long term concern over the code? http://www.dieselplace.com/forum/smileys/Approve.gif

I can answer your first question.


According to the “Transmission Times”http://www.dieselplace.com/forum/smileys/Cool.gif “P0733 Gear 3 Incorrect Ratio”

http://www.dieselplace.com/forum/smileys/Hug.gif A follow-up to my original post


When the dealer could not answer my questions (no surprises here) I finally found the time to call Allison, 1-800-252-5283. The tech rep was easy to get a hold of and eagerly answered all of my questions. If you have questions on the Allison I suggest you call the Allison Technical Assistance Line at the number above. Here is what I found:


The Allison TCM monitors several signals on both the input and output sides of the transmission and compaires them with one another. When is senses something different than what it expects to see it triggers the P0733 code, Gear 3 Incorrect Ratio, which in turn triggers the SES light.


When the P0733 code is active it prevents the transmission from shifting into 5th (OD) and keeps the torque converter from locking up. That explains why I thought the transmission was slipping and why I thought it would not go into OD. I was in a construction zone in the mountains so it was hard to tell if the transmission should have been in OD or not.


If, after one or two start-drive-shutdown cycles, the transmission does not detect a difference in the input - output readings from what it expects to see, the P0733 code will go inactive and the transmission will work normally. The P0733 code will remain in the TCM history for 40 start cycles and then it is erased. This also explaines why the transmission appeared to start working correctly after a couple of start-drive-shutdown cycles, however the SES light did not go out for a couple of days. Total start cycles from the original SES light came on until it went out on its own was about 10 to 15.


I think the informaion above is farily accurate, but not exactly what the tech rep said. Some of you might find this information usefull. http://www.dieselplace.com/forum/smileys/Thumbs Up.gif