Monday, June 04, 2012
Allison Automatic Transmission Retrieving Codes
The Allison Automatic Electronic Transmission offers a quick method to retrieve trans codes without requiring the Pro-Link reader. This is for older models before Allison required shops to have the DOC software to have any hope finding out what the fault is.
The video above is all about a preset code which in this case is losing the "output speed sensor" signal to the Trans ECU. I unplugged the sensor connector and once you try to move forward the transmission defaults into 1st gear. Without an output speed signal the ECU does not know where the transmission output speed is at... so it goes into this mode to protect the transmission because of the programming set up by Allison.
The output speed sensor can be checked out with an ohm meter which averages around 350 ohms depending on ambient temperature. Of course the wiring and connections is a step that should not be ignored. Any kind of resistance in the 30 foot harness running to the driver's cab will give a false signal. Opens and shorts are possible as well since the wiring is exposed to the environment. CHECK OUT THESE PREVIOUS POSTS ON THE ALLISON 3000 SERIES AUTOMATIC TRANSMISSION