Allison 3000 shift pad

biggy238

biggy238

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Aug 3, 2008
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I have a 2014 freightliner custom chassis with a customer complaint that the engine will not crank if the Trans shift pad displays the words " Allison transmission"
I'm making an educated guess that those two are only displayed when the D-pad has no communication with the TCU? And this would also mean that the TCU isn't broadcasting neutral interlock, and Inhibiting engine cranking?

Sound close? I don't have access to any Allison people, and can't duplicate the complaint here at the shop.

Thanks
Kyle
 
biggy238 said:
I have a 2014 freightliner custom chassis with a customer complaint that the engine will not crank if the Trans shift pad displays the words " Allison transmission"
I'm making an educated guess that those two are only displayed when the D-pad has no communication with the TCU? And this would also mean that the TCU isn't broadcasting neutral interlock, and Inhibiting engine cranking?

Sound close? I don't have access to any Allison people, and can't duplicate the complaint here at the shop.

Thanks
Kyle
Click to expand...

Most likely, we had a similar issue with Allisons in military trucks, you could run them until they were burnt to a crisp and ready to melt and it would work, once you went to neutral it gave you the big FU and it wouldn't shift from neutral until it was fixed...
 
That's awesome.

As soon as we gave it back to the customer it failed to crank the next morning. I got there while it was 19 degrees. I got under it and pulled the TCU connection. Inspected it and put it back, it cranked right up. I put it in their shop and put some dielectric grease on it.

I have absolutely no idea why it was temperature dependant.
 
Sounds to me like the TCM itself is losing power which then would lead to a no communication with the shift pad. You are able to pull DTC through the shift selector but are unable to see any inhibits. This you would need DOC for. Of course if the TCM was not powered up you would not be able to connect any way. Gen 4 displays would not be able to display words so I bet its gen 5. Only gen 5 units I've seen have been in paccar applications have not seen one yet in a freightliner chassy.
 
With the 4560 transmission we run in the concrete trucks we have found most of the time it is the TCU. Mostly only see issues with the older TID 2 units though. If you hit the up and down arrows on the keypads in our trucks at the same time you can pull up diagnostic info like low fluid, temperature, codes, etc..

You can send the controller to Weller truck parts and get them reflashed and checked out for relatively cheap.
 
The older tid2 units use a wire for each shift selector position. The newer gen 4 and gen 5 units use the trucks 1939 or CAN to relay the messages from tcm to selector.
 
I typed a reply but taper talk dumped it.
I needed you guys two weeks ago.
I agree that it was probably intermittent power supply. I think the connector was loose.
I checked for diagnostic codes first off and it didn't have any on 1708 or 1939, good indicator of a power problem.
 
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