07 allison ?

[ak diesel driver]

friend of mine has an 07 and has tranny troubles. He was towing heavy uphill when he heard a bang, he finished towing up the hill but discovered he was stuck in 3rd. now it's hit and miss sometimes it's fine othertimes it's stuck in 3rd. any thoughts? has codes po756 shift sel b, po848 press sensor switch, po700 control sys error.

 

[THEFERMANATOR]

P0700 just means teh TCM is requesting the check engine light to be on. Personally I would drop the pan and check the filter to make sure it isn't cracked or loose first. if it is and solid, then you probably have a valve body issue.