Nissan Genuine OEM Z32 300Zx VG30DE(TT) Power Transistor Unit The Nissan 300zx Power Transistor Unit controls the spark going into the engine. Most older cars or Japanese Spec engines have the older Power Transistor Unit that was recalled in the US. If you have the older unit with the Aluminum fins it is a very good idea to change it out for this updated unit in order to guarantee proper spark and fuel economy performance.