Cabin Coolant Heater (PTC (positive temperature coefficient) Heater) (Diesel equipped)
WARNING: This page is about a different car, the 2021 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
The cabin coolant heater has both low voltage and high voltage electrical connections. The low voltage circuits are used for controlling the unit, while the high voltage circuits are used for heating the coolant. The cabin coolant heater uses electricity, or more accurately, the heat for resistance in electrical circuits to quickly raise the temperature of the coolant to normal operating temperature. The PCM sends power to the cabin coolant heater and controls the PWM (pulse width modulation) circuit to the heater.