The code P20B1 comes when the car engine does not work properly. You need to get the real meaning of the code for solving the car engine. The automobile engineer needs to use manufacturer information about the code and that is necessary for solving the car engine. The manufacturer of the car sets specific meaning of the code for solving the car engine problem. The dictionary meaning of the code is P is Powertrain Code – Problem is related engine, transmission and emissions systems. 2 is MFG – Manufacturer Specific. 0 is Transmission. B for BBV Sensor Circuit Low Voltage and 1 for PCM Stack Overrun.