The car engine P2784 Code is found in many car engines but meanings of the code are not same. Because meanings of the code depend on the brand of the car. The car engine P2784 Code has general meaning and the general meaning is for all car engines but may not be suitable for your car engine problem. The general problem of this car engine code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 2 for MFG – Manufacturer Specific. 7 for Auxiliary Emission Controls. 8 for Exhaust Gas Recirculation System Valve 1 and 4 for Cruise Vehicle Speed/Set Speed Difference Too High.