A control system for a hybrid electric vehicle comprises a transmission system configured to drive wheels, an engine power subsystem connected to the transmission system, a motor power subsystem connected to the transmission system and a control module. When vehicle's electrical power is on, the control module is configured to control operating mode of the hybrid electric vehicle through the engine power subsystem and the motor power subsystem. The operating mode comprises HEV-eco mode and HEV-s mode. When the hybrid electric vehicle operates in HEV-eco and the hybrid electric vehicle operates at low power or when the hybrid electric vehicle operates in HEV-s mode and when the vehicle speed is zero, the control module enables the hybrid electric vehicle to operate by idle start-stop strategy.

A method (500) and apparatus (10-5) for carrying out the method of mitigating fuel in oil in an internal combustion engine of a hybrid electric vehicle, the method comprising: determining an amount of fuel flow into the engine oil during one or more cold start phases of engine operation (505); determining an amount of fuel flow into the engine oil during one or more enrichment phases of engine operation (510); determining an amount of fuel evaporated from the engine oil during one or more phases of vehicle operation with the engine on (515); determining an amount of fuel evaporated from the engine oil during one or more phases of vehicle operation with the engine off (520); determining a percentage of fuel in the engine oil from the amount of fuel flow into the engine oil and the amount of fuel evaporated from the engine oil (525); and modifying vehicle operation based on the percentage of fuel in the engine oil exceeding a first fuel in oil threshold or a second fuel in oil threshold (540).