The engine P1643 code briefly explains about the car engine problem and from the engine code, it seems that this is the kind of powertrain problem. The automobile dictionary meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 1 for MFG – Manufacturer Specific. 6 for Vehicle Speed Control And Idle Control System. 4 for BBV Sensor Circuit Low Voltage and 3 for Transmission Control Module Reprogrammable Memory. These are automobile dictionary meaning of the code what provide general information of the car engine problem but you must not rely on the general meaning what make terrible problem in future.