GM Duramax Allison trans problems (1 Viewer)

FJ40Jim

The Cruiser Whisperer
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My neighbor has an '06 Silverado 2500HD, 4x4, Dirtymax, allison auto trans, 138K miles. I borrow/rent this truck when I need to tow/haul heavy stuff. The problem the trans is exhibiting is "morning sickness": won't shift out of 2nd or 3rd gear on cold mornings. The MIL illuminates when this happens. If it warms up the tranny will eventually start to shift as normal. Fluid quantity & quality is good.

The codes are:
P0700
P0846
P0847
P0841

I thought the allison was indestructible. Are these common codes/symptoms? Any common/easy fixes?
 
Joined
Sep 18, 2014
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west coast, us
Those are all pressure switch codes. The pressure switch is located on the outside of the valvebody right under the pan. Drop the pan and the pressure switch is right there. Check the o-rings underneath and the wiring.
 

FJ40Jim

The Cruiser Whisperer
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Thanks for the reply. Owner had fluid & filter changed and problem seems to have self-corrected once we got through the coldest couple weeks of winter. I'm pretty sure that the prob will recur next winter, but it's not my truck so we'll wait & see.
 

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