The P20A4 Code comes while the car engine is tested. Do not drive the car with the fault of the car engine. The dictionary meaning of the code is P for Powertrain Code – Problem is related engine, transmission and emissions systems. 2 for MFG – Manufacturer Specific. 0 for Transmission. A for BBV Sensor Circuit Low Voltage and 4 for Cruise Vehicle Speed or Set Speed Difference Too High. The general information of the code is not necessary for solving the car engine. You have all necessary information if you read the manufacturer information according to the manual of the car.