NEED HELP! Having some weird transmission issues

CCLB06

New member
Jan 4, 2020
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Ohio
I have been chasing this issue for awhile now. My range selector light underneath (PRNDM1) will only light up under Park, Nuetral and Manual. Also when this happens I have no reverse lights. It has also intermittently displays range shift inhibited on the DIC, when this happens I shut the truck down restart it and it’s fine after.

Last night I was driving I shifted it from manual to Drive and it’s like it went to Nuetral so I shift back to manual and same thing it’s like Nuetral. I pull over on the high way shift to park back to drive and it’s sluggish so I shift to manual and it’s stuck in 4th gear, I drove to the nearest exit and shut the truck down restarted it and it’s Fine.

I have searched the forums and watched YouTube videos and everything talks about these issues on the 5 speed Allison’s and not the 6 speed Allison’s.

Pulled the codes and it came back with P0722, P0708
 

Mike L.

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Aug 12, 2006
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708 is a internal mode switch. very rare for them to go out. 722 code is speed sensor code. No way to check TCM except to put a known good one on and see if problem goes away.
 

CCLB06

New member
Jan 4, 2020
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Ohio
708 is a internal mode switch. very rare for them to go out. 722 code is speed sensor code. No way to check TCM except to put a known good one on and see if problem goes away.
Okay, I have a new genuine Allison internal mode switch. ( sorry forgot that’s what they are called for the 6 speed Allison’ ). I bought awhile ago because I was having this issue before and it quit doing it for a few months, now all a sudden the problem is back.

I am thinking I need to start looking for wires that might be damaged or even check the pass through connector on the passenger side of the trans to see if it’s full of trans fluid or any kind of gunk.
 

CCLB06

New member
Jan 4, 2020
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Ohio
Well I think I am going to get a new TCM, I am looking at the dans diesel TCM and Ryan’s diesel service TCM.

Any other recommendations?
 

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