How is a PO700 Code diagnosed and resolved

Question

I am having problems with my transmission. It is not steady but occasional. My mechanic through the OBD found this PO700 code. I get a "service engine soon" light and the transmission does not change gears and in some cases does not move in drive and sometimes reverse. The "service engine soon" light will go off and the truck will run like new for a week and then the problem comes back for a day. When I have this issue I shut the truck off and start it up and put it in drive and she runs good even with the "service engine soon" light still on. Eventually the truck runs like new for a time before the shifting of gears triggers the light to come on.  It is a Allison transmission so maybe it could be a sensor or loose wire, I don't know

Answer 1

P0700 Transmission fault detected MIL light requested

Different scan tool read out codes different. P0700 . By using a different scan tool you may get a exact code condition, With this type of engine having the TCM (Transmission control module) at the front , when ever the radiator is replaced the TCM is disconnected, its pin at the TCM gets faulty so will have to check the pins at the TCM, Having a Alilson transmission the reaction sun shell in the transmission tends to not be able to hold properly as a result you would experience no reverse, no second gear , and no fourth gear, To find out if this is the problem when the condition occurs, Check to see if you would have movement in first gear, as well as third, if so you have a internal transmission problem with the reaction sun.