Most of us do the copying and writing using a bench harness though not everybody. Doing it in the vehicle has risks of the DC voltage in the vehicle battery going too low or bus chatter noise from other modules interfering with the writing.

My bench harness is entirely constructed of junk yard parts supported by a good 13.8 volt, three amp Radio Shack power supply. A wall wart 12 volt supply is also risky for too little amperage or an unstable voltage. Fortunately, I have never bricked a PCM but it would be a good intellectual exercise someday to see if I could unbrick it.

Rick