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 module 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 aluminum.
The heating elements only cut in when there are sufficient electrical power reserves. The DDE control module determines the present reserves of power in the vehicle electrical system. The DDE control module informs the control module 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 memory of its own. All faults are stored in the IHKA control module.
The DDE control module monitors the line for the message regarding reserves of power.