One problem related to power train has been reported for the 2003 Volkswagen GTI. The most recently reported issues are listed below.
Hard downshifts from 4th gear to 2nd gear to 1st gear cause vehicle to slow abruptly and without warning. When approaching a red light or stop sign, transmission shifts unexpectedly from fourth to second gear and then to first gear with no warning to vehicle behind (not breaking heavily) causing near collisions. Five speed automatic transmission with tiptronic feature causes sudden deceleration endangering occupants with possible collision with trailing vehicle.