Network Message Chart - Module Network Input Messages

Cabin Coolant Heater System Operation 

The cabin coolant heater system provides warm coolant to the heater core to warm the passenger compartment whenever the front HVAC control module requests heat and the vehicle is in a driving mode, remote started, or doing Cabin DriveConditioning. A SOBDMC controlled cabin coolant heater warms the coolant. The cabin heater coolant diverter valve allows two modes: Either an isolated coolant loop with cabin coolant heater, heater core, and cabin heater coolant pump or a combined loop of those components along with the engine and other coolant components. A cabin heater coolant temperature sensor in the cabin heater system provides the PCM with coolant temperature information.

Electric Booster Heater Operation 

The electric booster heater ensures that the passenger compartment can be quickly warmed up when ambient temperatures are low. It is a heater element made up of ceramic resistors that is mounted in the climate control housing. It directly heats the airflow into the passenger compartment rapidly in the case of low ambient temperatures.

The current is switched via three electric booster heater relays located in the BJB. The electric booster heater power and ground is supplied via a plug-in connection.

The FCIM energizes the electric booster heater relays when the operating parameters have been met. The electric booster heater relays are activated or deactivated individually or together by the FCIM as needed.

Electric booster heater operating parameters:

• Engine is running
• HVAC controls have been switched to the highest temperature setting
• Engine coolant temperature is below approximately 75 deg.C (167 deg.F)
• Ambient air temperature is below approximately 12 deg.C (53.6 deg.F)
• Sufficient generator capacity is available

The electric booster heater is deactivated when an engine coolant temperature of approximately 85 deg.C (185 deg.F) or an ambient air temperature of approximately 15 deg.C (59 deg.F) is exceeded.

Component Description

Electric Booster Heater 

The electric booster heater, also known as the PTC heater, is made up of three separate ceramic resistor elements.

Cabin Heater Coolant Pump 

The cabin heater coolant pump is controlled by the PCM and provides coolant to the cabin coolant heater system while the vehicle is in a driving mode, remote started, or doing Cabin Drive-Conditioning.

Cabin Coolant Heater (PTC Heater) 

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 SOBDMC sends power to the cabin coolant heater and controls the PWM circuit to the heater.

Cabin Heater Coolant Temperature Sensor (PTC Heater) 

The cabin heater coolant temperature sensor is connected to the PCM. The sensor provides the coolant temperature information to the PCM.

Heater Core 

The heater core consists of fins and tubes arranged to extract heat from the engine coolant and transfer the heat to air passing through the plenum.

Cabin Heater Coolant Diverter Valve 

The default state of the cabin heater coolant diverter valve is de-energized, placing the system in combined loop mode. Coolant flows out of the engine, then back, in the following order:

• cabin heater coolant pump
• cabin coolant heater
• cabin heater coolant temperature sensor
• heater core
• cabin heater coolant diverter valve
• thermostat housing
• main electric water pump

When energized by the PCM the cabin heater coolant diverter valve places the system into the isolated loop mode. Coolant flows out of the valve, then back, in the following order:

• cabin heater coolant pump
• cabin coolant heater
• cabin heater coolant temperature sensor
• heater core