A method for controlling an internal combustion-cabin heater coolant circuit for a plug-in hybrid electric vehicle, the vehicle comprising an internal combustion engine, a coolant outlet of the internal combustion engine being connected to a coolant inlet of a fuel operated heater and wherein a coolant outlet of the fuel operated heater is connected to a coolant inlet of an HVAC heater, a coolant outlet of the HVAC heater further being connected to a coolant inlet of the internal combustion engine, the vehicle further comprising a temperature sensor arranged at the coolant outlet of the internal combustion engine and a temperature sensor arranged at the coolant outlet of the fuel operated heater, the vehicle further comprising a three way valve arranged between the coolant outlet of the HVAC heater and the coolant inlet of the internal combustion engine such that there is a connection between the coolant outlet of the HVAC heater and the coolant inlet of the fuel operated heater, the connection thus bypassing the internal combustion engine, the circuit comprising an electrical pump, the vehicle further comprising a climate system control unit, an internal combustion engine control unit, and an ambient temperature sensor, the method comprising,
- monitoring the ambient temperature,
- if the vehicle is in electric drive and the ambient temperature is below or equal to 15° C. and above or equal to 0° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the fuel operated heater and the electrical pump and request closing of the valve to direct coolant flow through the connection to bypass the internal combustion engine, and thereafter, if a certain operation time has passed or if the coolant outlet temperature of the fuel operated heater is less than a temperature (Y) corresponding to a temperature which is less than a coolant outlet temperature of the fuel operated heater for which half power/capacity operation the fuel operated heater is to be requested, request partial opening of the valve to allow partial coolant volume flow through the valve to the internal combustion engine while at least some coolant flow through the connection remains,
- if the vehicle is in electric drive and the ambient temperature is below 0° C. and above −40° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the internal combustion engine and start of the fuel operated heater and start of the electrical pump where the valve control will be aimed to optimally fulfil the internal combustion engine and the climate system thermal targets considering the vehicle fuel consumption and its electrical drive feasibility,
- if the vehicle is in electric drive and the ambient temperature is equal to or below 15° C. or above −8° C. and the coolant outlet temperature of the internal combustion engine is lower than the coolant outlet temperature when the fuel operated heater is requested to start, request start of the fuel operated heater and start of the electrical pump and request closing of the valve to direct coolant flow through the connection to bypass the internal combustion engine,
- if the vehicle is in electric drive and the ambient temperature is equal to or below 15° C. or above −8° C. and the coolant outlet temperature of the internal combustion engine is higher than the coolant outlet temperature when the fuel operated heater is requested to start, request start of the electrical pump but not the fuel operated heater and request opening of the valve,
- if the vehicle is in electric drive and the ambient temperature is below 0° C. and above −40° C. and the coolant outlet temperature of the fuel operated heater is higher than the temperature when the internal combustion engine is requested to start, request start of the fuel operated heater and electrical pump where the valve control will aim to optimally fulfil the internal combustion engine and the climate system thermal targets considering the vehicle fuel consumption and its electrical drive feasibility,
- if the vehicle is in electric drive and the ambient temperature is below 0° C. and above −40° C. and the coolant outlet temperature of the fuel operated heater is lower than the temperature when the internal combustion engine is requested to start, request start of the internal combustion engine, start of the fuel operated heater, and start of the electrical pump where the valve control will aim to optimally fulfil the internal combustion engine and the climate system thermal targets considering the vehicle fuel consumption and its electrical drive feasibility,
- if the vehicle is in hybrid drive and the ambient temperature is equal to or below 15° C. and above −40° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the fuel operated heater and start of the electrical pump and request opening of the valve,
- if the vehicle is in hybrid drive and the ambient temperature is equal to or below 15° C. and above −40° C. and the coolant outlet temperature of the internal combustion engine is higher than the coolant outlet temperature when the fuel operated heater is requested to start, request opening of the valve but do not request start of either the fuel operated heater or the electrical pump,
- if the vehicle is in hybrid drive and the ambient temperature is equal to or below 15° C. and above −40° C. and the coolant outlet temperature of the internal combustion engine is lower than the coolant outlet temperature when the fuel operated heater is requested to start, request start of fuel operated heater and start of electrical pump and request opening of the valve,
- if the vehicle is in an internal combustion engine driving mode and the ambient temperature is equal to or below 15° C. and above −40° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the fuel operated heater and start of the electrical pump and request opening of the valve,
- if the vehicle is in an internal combustion engine driving mode and the ambient temperature is equal to or below 15° C. and above −40° C. and the coolant outlet temperature of the internal combustion engine is higher than the coolant outlet temperature when the fuel operated heater is requested to start, request opening of the valve but do not request start of either the fuel operated heater or the electrical pump,
- if the vehicle is in an internal combustion engine driving mode and the ambient temperature is equal to or below 15° C. and above −40° C. and the coolant outlet temperature of the internal combustion engine is lower than the coolant outlet temperature when the fuel operated heater is requested to start, request start of fuel operated heater and start of electrical pump and request opening of the valve,
- if the vehicle is in a hybrid or an internal combustion engine driving mode and the ambient temperature is above or equal to 25° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump,
- if the vehicle is in a hybrid or an internal combustion engine driving mode and the ambient temperature is above or equal to 25° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine is higher than the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump,
- if the vehicle is in electrical drive and the ambient temperature is above or equal to 25° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump,
- if the vehicle is in electrical drive and the ambient temperature is above or equal to 25° C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine is higher than the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump.