Grim289 Posted April 5 Share Posted April 5 I have a 2006 cxn with an ac400 and allison transmission. Today everything seemed fine all day nothing unusual happened until I was on my way home. The transmission shifted itself into neutral and the shifter on the dash went blank. It came back on but had a star pattern for a few moments and went to flashing 6. I pressed the neutral button and then put it back into drive. It would go up to 3rd then shift hard into neutral and the control panel would start flashing. It is full of trans fluid and no blown fuse. Any help would be appreciated. Any leads would be helpful to begin the diagnostic process Quote Link to comment https://www.bigmacktrucks.com/topic/74028-allison-transmission-problems/ Share on other sites More sharing options...
JoeH Posted April 7 Share Posted April 7 How many miles and which auto trans is in it? Quote Link to comment https://www.bigmacktrucks.com/topic/74028-allison-transmission-problems/#findComment-549540 Share on other sites More sharing options...
JoeH Posted April 7 Share Posted April 7 Brief googling, the flashing 6 is probably because it has a shift inhibitor, it won't let you put it into drive while moving. So it locks you in neutral until the controller deems it safe to change shifter range. It probably had a drop in power that rebooted the transmission computer. Could be faulty wiring, weak circuit breaker/fuse contacts, drop in communication between different computers, etc. The shift display going blank makes me think the power supply dropped out briefly, shutting off the transmission controller. If your truck is anything like my MR688 with AI350 and an Allison HD4560, then the transmission should have a "clean power" (independent power supply directly off one of the batteries) supply via positive and negative wires that has a fuse in the battery box on the positive wire. Maybe you'll find fault with this wire. CleanPower means a power source independent of any other circuits, it's directly off the battery so the transmission has full battery voltage without possibility of voltage fluctuations from sharing power supply. Quote Link to comment https://www.bigmacktrucks.com/topic/74028-allison-transmission-problems/#findComment-549589 Share on other sites More sharing options...
The Heinz Posted April 8 Share Posted April 8 I'm not well acquainted with "older" Allisons, but if your transmission has a TCM, it could be that. We've seen many failures of newer modules, sometimes even in brand new trucks. If you have one, it's usually found behind the center dash. I'd first try the wiring diag before you sling parts at it. Quote Link to comment https://www.bigmacktrucks.com/topic/74028-allison-transmission-problems/#findComment-549623 Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.