The electric auxiliary heater heats the coolant with electric heating elements to compensate for the slight heat loss at high degrees of engine efficiency. The heat power request comes from the air conditioning system (IHKA).
The electrical auxiliary heater and its control unit are components of the heat exchanger for the heating system in the air-conditioning system. The refrigerant-cooled heater fins have been supplemented by electrically heated heat exchanger elements made of aluminium.
The heating elements only cut in when there are sufficient electrical power reserves. The DDE control unit determines the present reserves of power in the vehicle electrical system. The DDE control unit informs the control unit of the electrical auxiliary heater by means of a PWM signal of the maximum additional electrical power.
The electrical auxiliary heater has a self-diagnosis function, but no fault code memory of its own. All faults are stored in the IHKA control unit.
The DDE control unit monitors the line for the message regarding reserves of power.