The automobile dictionary meaning of the car engine P2791 Code is found from online and it is p for Powertrain Code Problem is related engine, transmission and emissions systems. 2 for MFG – Manufacturer Specific. 7 for Auxiliary Emission Controls. 9 for Crankshaft Position Sensor Circuit Performance and 1 for TFP Valve Position Switch-Drive Without Drive Ratio. The meaning of the car engine code is important to understand the problem and real meaning of the code is the best thing for understanding the actual problem. When the car engine is found fully ok and you have tested the car engine, you can accept it for drive.