explanation of limp home mode
What is "limp-home mode" ? This is a fault mode in which the transmission either loses electrical power or the PCM deactivates all of the electronics. The transmission will default to max line pressure. The driver will have Reverse and 3rd, with manual 2nd available by putting the gearshift in 2 or 1 (doesn't matter). 1st, 4th, and TCC lockup will not be available. It will not hurt the car to drive it like this for short periods, but use manual 2nd to get the car moving, and be aware that the trans will generate more heat than normal while operating in limp-home mode due to increased torque converter slippage during 2nd gear starts and no lockup in 3rd gear. This explains the scanmaster shutting down and all that, just have to figure out why the PCM is shutting down.
also note did you check the fuses, the #5 fuse for the PCM in the U/H panel labeled TRANS sends power to the PCM as well as the Trans, FSM states that it only powers the PCM for ignition feed, but not exactly sure if that is entirely true as I don't have the internals to the PCM where as if it would run if this fuse was blown and the PCM would get the power from elsewhere. Still digging.