Some modules which have permanent power will scan with the ignition off, it's module dependent - if a module scans with the ignition off it's nothing to be concerned abo
The reason I asked is iv got a a3 3.2 Quattro in with a strange electrical issue. Most of the time the car works fine, but sometimes the dash will not light up its (totally dead) and car wont start then 10-20min later its fine again. When I try to do a scan when its playing up the only thing VCDS can communicate with is the engine ECU. Anyway totally by accident i found i could scan the engine ECU with the ignition off but nothing elsei have tried to scan without ignition on ( sometimes I am in rush ) ( except those cars with electronic steering lock ) but no ecu ever responded.