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Discussion Starter · #1 ·
I have an 2002 3500 LB7 with a stock Allison and I am having an issue only in the mornings on initial startup of the truck will not move in any gear (gear flashes on dash) if I let the truck warm up to operating temps of 160-170 ECT then clear the code with my Edge rev the engine a few times I can get the truck to move and it will continue running normal all day (average 175-200 miles/day) then park the truck at night then go back out in the A.M. and do it all again. Yesterday I replaced the NSBU switch started the truck and it drove fine but then this morning I had the same issue all over again. Brought it to the shop and they can not get the reader to communicate with the transmission, it will communicate with the engine and ABS just not the tranny.
Any thoughts?
 

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Discussion Starter · #2 ·
Ok so I was able to get the tranny and the Snap on to communicate - I am getting a P0841 and a P0875. Any suggestions on what to do next. THANK YOU
 

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Please let me know how you fix yours. It sounds like we have very similar problems. mine pulls codes po875 and p0843. The crazy thing with mine is it wont do it all the time. Mainly in the mornings. its crazy
 

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my dads lly is doing the same thing when cold, if you let it warm up a little its fine, also has a new nsbu switch
sounds like valve body could be getting stuck or gummed up
 

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Discussion Starter · #6 ·
Mine is only in the morning or if it sits for more then 2 hrs and the outside temps are below freezing. Still no solution. Tranny shop is researching codes and talking with Allison manufacturing. I'll keep you posted.
I have also heard possible valve body but I'm tired of throwing parts at it and not being the issue.
 

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Here is where I am with my issue/diagnosis:

OK, update to where I'm at. I was able to get the NSBU switch from a local Allison dealer for less than 80 bucks. I put it on Monday afternoon and no change to the condition.

I am not surprise by that but it eliminates a variable. I was able to disconext the Trans connector on a suggestion from another thread and it does go into limp mode now. Shifts very hard into reverse and forward (3rd). Of course I got all kinds of warnings and a bunch of codes now about every solenoid and over temp etc.

Does this tell us anything? For me it eliminates the transmission pump losing prime as well since it goes in forward and reverse gears.
 

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Discussion Starter · #8 ·
I too replaced my NSBU with no change. Seems that once I get the tranny fluid temp to 100 degrees and restart the truck it comes out of limp mode and runs fine until it sits and cools down. The tranny shop is dropping the pan tomorrow to take a look. He seems to believe from reading the bulletins it has to do with some pressure switch. I'll let you know what happens tomorrow.
 

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What did you find out was the problem. I am having the same problems in the morning.
 

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Discussion Starter · #10 ·
So yesterday I took my truck to the tranny shop and they drop the transmission pan and what they found was the filter sitting in the bottom of the pan. It had come disconnected and that was the cause of my problem. They replaced both filters and all the fluid. This morning I went out and started my truck temperatures 30° in the truck started moving right away no issues
 

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Discussion Starter · #11 ·
He also created a bracket to prevent the filter from coming disconnected again. For some reason the filter did not touch the pan which is supposed to hold it in place. He thinks the design of the new filters maybe slightly thinner than the original design allowing there to be room for movement which caused it to come disconnected from hitting potholes and bumps
 

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so thanks a ton, my dad just pulled his pan and sure enough exact same thing

any pics of the bracket you made by chance? we are going to use the suncoast allison filter lock on ours
 
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