How do you tell whether the ECU has been moded from a visual inspection.Does the lettering GIAC appears on the inside of a oem ECU?Since the ECU are made by Bosch,i would assume GIAC would be the aftermarket tuners signature?

 

You can't visually.. unless it's like over 2.5 years old before the days of flashing. Drive the car and if you're getting .9-1.0 bar you have a chip of some sort. Or open the box up and see if there's a daughter card or "non-factory" soldering.. That's a good sign.