Is there a published list of codes online anywere? I am looking for P1720- I know it is for the transmision. I`d rather not pay a dealer $100 to scan the truck. The trans is locking out 5th gear after 140 kmh (under load of course).

http://www.dieselplace.com/forum/showthread.php?t=22718

or this


http://www.dieselplace.com/forum/dtc.php

Thanks, I tried searching before but couldn`t find any info.

The code says; Solenoid A Controlled Clutch Stuck Off. Any idea what that means?

A P1720 is Solenoid A Controlled Clutch Not Engaged.

There are two trim solenoids that apply pressure to the five clutches in the Allison: Solenoid A controls the C1, C3 and C5 clutches while Solenoid B controls C2 and C4 (you need two active clutches to make the truck go, three to break it). Basically what this code means is that Solenoid A was commanded to apply pressure to a clutch and either it applied the pressure too slowly or the clutch would not fully engage. It's likely the result of a stuck valve. If it only happened once I wouldn't worry about it, likely a small piece of debris that will eventually end up in the filter. If it's happening regularly it needs to be checked out.

Thanks Machinator. This has happened twice in two weeks. I will go and get the trans flushed/filter changed and see if that helps. If I have to get it checked out should I go to the dealer or an Allison service center?

If it's out of warranty I'd see if there's a Detroit Diesel-Allison distributor in your area that could do the work (Allisontransmission.com has a locator). They should be cheaper and more experienced.

Looks like there is two dealer/service depots near me. They say about $250 for a transynd/filter change. Another $100 for internal filter. They said that they can test and change the valves if ness. The service rep also said that they are not allowed to rebuild Allison tranys with aftermarket parts :( ie. suncoast. ( I asked just in case I need to rebuild, which by all accounts I should anyway if I want to play.):)