The car engine P1728 Code has many meanings and you should not choose any meaning of the code for solving the car engine. The automobile dictionary meaning of the code is found online and many automobile engineer also use that meaning for solving the car engine. The automobile dictionary meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 1 for MFG – Manufacturer Specific. 7 for Auxiliary Emission Controls. 2 for Air Conditioning (A/C) Clutch Feedback Circuit High Voltage and 8 for PCM Stack Overrun but you must give priority to the real meaning of the engine code.