This engine P2478 Code helps to locate the problem and understand the car engine problem. The problem of the car engine is not difficult to solve if the problem of the engine is powertrain. The letter P means powertrain and it is easy to solve. Every parts of the car engine code is meaningful and you need to know the full meaning of the code to understand the right meaning. The general meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 2 for MFG – Manufacturer Specific. 4 for Transmission. 7 for Vehicle Speed Output Circuit and 8 for PCM Stack Overrun.