The automobile dictionary meaning of the P0021 Code is available online and it is not helpful for solving the car engine problem. If this meaning of the code is used for solving the car engine problem, you may face more terrible problems. The general meaning of the code is P for Powertrain Code Problem is related engine, transmission and emissions systems. 0 for SAE – Generic. 0 for Fuel And Air Metering. 2 for Air Conditioning (A/C) Clutch Feedback Circuit High Voltage and 1 for TFP Valve Position Switch-Drive Without Drive Ratio. The engine code comes for the powertrain problem from the car engine.