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 Allison transmission trouble shooting
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Jay Graham
New Member

7 Posts

Posted - 05/11/2013 :  4:19:32 PM  Show Profile  Reply with Quote
Our school has a 2007 IH bus with dt466 and 2500pts Allison trans. It developed a problem on route yesterday and would no longer drive the bus. When I arrived at the bus, it would not start due to a suspected neutral safety switch issue. After jumping across the solenoid and getting the engine started, the bus had both forward and reverse movement. I was able to drive the bus to the shop, but it would not shift out of what appeared to be possibly second gear. The next sympton is no speedometer. No fault codes appeared when I attached the scan tool. I assume the bus is in limp in mode and the no speed indication also causing the no shift. Am a bit puzzled as to the relation of the neutral safety switch issue and the speed sensor. Since both the Neut safety switch appears to be on the right rear of the trans, I am wondering the the speed sensor wheel has broke and pieces have attacked the neutral safety switch. Fluid if full , but does look discolored, but does not smell burnt. Bus has nearly 80,000 miles on it. Also appears to be a possible leak at the left rear corner of the pan at the gasket. Any ideas out there??? Any help would be greatly appreciated!!! Thanx in Advance!!!

tigger2
Advanced Member

USA
281 Posts

Posted - 05/13/2013 :  04:19:18 AM  Show Profile  Reply with Quote
One of the local wreckers I work on has a similer problem, when I hooked up the scan tool there was no ign. voltage to the transmission. All fuses checked out and we jumped the relay for nuetral switch to move the unit. I am waiting on a scematic on the K-W wiring.
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BLUEBIRD1965
New Member

5 Posts

Posted - 05/19/2013 :  08:28:37 AM  Show Profile  Visit BLUEBIRD1965's Homepage  Reply with Quote
The ECM fuse from the battery up to 2005 have been burning out. Even if the fuse and holder seem fine, its normally been found to be our problem, we replace it.
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mastertech
Advanced Member

228 Posts

Posted - 05/19/2013 :  6:09:48 PM  Show Profile  Visit mastertech's Homepage  Reply with Quote
We have seen plenty especially lately of the power cables that run forward towards the starter rubbing through on the sharp edged brackets that are suppossed to keep them protected. You lose power to the tcm and the tranny reverts to reverse and 4th gear only. You will get a code in the bcm for low data rate or no data from the tcm which will not let the bus start because it cant get a neutral signal. Forcing the bus to run in this gear will barbeque the torque converter especially in town driving so fix it quick. If you can get comunications to the tcm then it may have just a corroded speed sensor connector which will give you codes. . There are 3 of them on top the tranny. Look for green rot deep in the sensors pins. The allison software has all the allison pinouts in it and you can get all the wiring diagrams off isis bus schematics.
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