The engine P0666 Code is supporting content but do not use wrong meaning of the code for fixing the car engine. The automobile dictionary meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 0 for SAE – Generic. 6 for Vehicle Speed Control And Idle Control System. 6 for Control Module Throttle Actuator Position Performance and 6 for Cruise Control System – Vehicle Accel Too High. Read the manual of the car engine to know the real meaning of the code and you should find the real meaning by the name of the car and manufacturer.