Fuel Fired Booster Heater (Non NAS)

Operation of the Fuel Fired Booster Heater (FFBH) is controlled by a status message from the ATCM (Automatic Temperature Control Module) to the Fuel Fired Booster Heater Control Module (FFBHCM). A similar status message, from the Fuel Fired Booster Heater Control Module (FFBHCM) to the ATCM, advises the ATCM of the current operating status of the FFBH.

While the engine is running, if the ambient air temperature is less than 7°C (45°F) (Diesel) or 1°C (34°F) (Petrol) and the engine coolant temperature is less than 75°C (167°F) the ATCM changes the status message from 'heater off' to 'supplemental heat'. The FFBHCM then changes the status message it sends the ATCM to 'supplemental heat' and starts the FFBH.

If the engine is started and the FFBH is requested. The ATCM closes the recirculation flap for the first 4 minutes or until the vehicle road speed exceeds 16 km/h (10 mph). The ATCM opens the recirculation flap to enable the ingress of fresh air. This feature is over ridden if the MAX demist switch on the Integrated Control Panel (ICP) is selected or if the ATCM detects a risk of misting of the windshield.

The FFBH will not start, or will discontinue operation, if any of the following occur:

• The FFBHCM is in the error lockout mode (see DIAGNOSTICS below).
• The engine stops running for approximately 4 seconds. The time delay is included for stall detection.
• The ATCM receives a 'fuel cut-off' message from the Body Control Module/Gateway Module (BCM/GWM) on the High Speed (HS) Controller Area Network (CAN) comfort systems bus. The BCM/GWM sends the message if it receives a crash signal from the RCM (Restraint Control Module).

  For additional information, refer to: AIRBAG AND SAFETY BELT PRETENSIONER SUPPLEMENTAL RESTRAINT SYSTEM .

• The ATCM receives a low fuel level message from the BCM/GWM on the HS CAN comfort systems bus.
• The Quiescent Current Control Module (QCCM) integrated into the Rear Junction Box (RJB) disconnects the power supply to the FFBH.

  For additional information, refer to: BATTERY AND CABLES .

If the FFBHCM does not start the FFBH, or discontinues operation, the status message to the ATCM remains at, or changes to, 'heater off'.

If the ambient air temperature increases to 10°C (50°F) (Diesel) or 4°C (40°F) (Petrol) or the engine coolant temperature increases to 88°C (190°F) The ATCM cancels supplemental heating, by changing the status message to the FFBHCM back to 'heater off'. The FFBHCM then cancels FFBH operation and changes the status message to the ATCM to 'heater off'.

Start Sequence 

At the beginning of a start sequence, the Fuel Fired Booster Heater Control Module (FFBHCM) energizes the Fuel Fired Booster Heater (FFBH) coolant pump then operates the following in a preset sequence to start the FFBH:

• The combustion air fan
• The glow plug
• The FFBH fuel pump.

Once combustion has stabilized, the FFBHCM switches off the glow plug. If the FFBH fails to ignite the FFBHCM repeats the start sequence.

Combustion Loads 

While the Fuel Fired Booster Heater (FFBH) is running, the Fuel Fired Booster Heater Control Module (FFBHCM) depending on the temperature of the coolant in the heat exchanger cycles between:

• Power load combustion
• High load combustion
• Low load combustion
• A control idle phase of operation.

The heat output level at low load combustion is 2.3 kW. This rises to 5 kW at high load combustion and 5.2 kW at power load combustion. The FFBHCM transmits the amount of fuel used by the FFBH to the Body Control Module/Gateway Module (BCM/GWM), and the FFBH coolant temperature to the ATCM (Automatic Temperature Control Module).

Switching Point Temperatures 

The switching point temperatures are for reference only and may vary depending on the fuel type and engine size.

After the start sequence, the Fuel Fired Booster Heater Control Module (FFBHCM) maintains power load combustion until the coolant temperature reaches switching point temperature 1  . At this temperature, the FFBHCM decreases the speed of the Fuel Fired Booster Heater (FFBH) fuel pump and the combustion air fan to enable high load combustion. The FFBHCM maintains high load combustion while the coolant temperature remains between switching point temperatures 2  and 6  .

At high load combustion the temperature of the coolant will increase or decrease depending on the amount of heat required to heat the vehicle interior. If the coolant temperature decreases to switching point temperature 6  , the FFBHCM increases the speed of the FFBH fuel pump and the combustion air fan to full speed, to return to power load combustion. If the coolant temperature increases to switching point temperature 2  . The FFBHCM decreases the speed of the FFBH fuel pump and the combustion air fan to enable low load combustion.

At low load combustion the temperature of the coolant will again increase or decrease depending on the amount of heat required to heat the vehicle interior. If the coolant temperature decreases to switching point temperature 5  . The FFBHCM increases the speed of the FFBH fuel pump and the combustion air fan to enable high load combustion. If the coolant temperature increases to switching point temperature 3  , the FFBHCM enters a control idle phase of operation.

On entering the control idle phase, the FFBHCM immediately switches the FFBH fuel pump off, to stop combustion, and starts a timer for the combustion air fan. After a 90 seconds (diesel vehicles) or 120 seconds (petrol vehicles) cool down period. The FFBHCM switches the combustion air fan off and then remains in the control idle phase while the coolant temperature remains above switching point temperature 4  . If the coolant temperature decreases to switching point temperature 4  , the FFBHCM initiates a start to low load combustion.

Shutdown 

To stop the Fuel Fired Booster Heater (FFBH), the Fuel Fired Booster Heater Control Module (FFBHCM) de-energizes the FFBH fuel pump to stop combustion. The combustion air fan and the coolant pump continues operation for a time, to cool down the FFBH. The cool down time is approximately 90 (diesel vehicles) or 120 (petrol vehicles) seconds.

Diagnostics 

The Fuel Fired Booster Heater Control Module (FFBHCM) monitors the Fuel Fired Booster Heater (FFBH) system for faults. Any faults detected are stored in a volatile memory in the FFBHCM, which can be interrogated by Land Rover approved diagnostic equipment via the Medium Speed (MS) Controller Area Network (CAN) comfort systems bus. A maximum of three faults and associated freeze frame data can be stored at any one time. If a further fault is detected, the oldest fault is overwritten by the new fault.

The FFBHCM also incorporates an error lockout mode of operation that inhibits operation to prevent serious faults from causing further damage to the system. In the error lockout mode, the FFBHCM immediately stops the FFBH fuel pump, and stops the combustion air fan and coolant pump after the cool down time. Error lockout occurs for start sequence failures, combustion flameouts, heat exchanger casing overheat and if the primary battery voltage is out of limits.

• Start failure and flameout: If a start sequence fails to establish combustion, or a flameout occurs after combustion is established, the FFBHCM immediately initiates another start sequence. The start failure or flameout is also recorded by an event timer in the FFBHCM. The event timer is increased by one after each start failure or flameout, and decreased by one if a subsequent start is successful. If the event timer increases to three (over any number of drive cycles), the FFBHCM enters the error lockout mode.
• Heat exchanger casing overheat: To protect the system from excessive temperatures, the FFBHCM enters the error lockout mode if the heat exchanger coolant temperature exceeds 125°C (257°F).
• Battery voltage out of limits: Error lockout will occur if the primary battery voltage is outside the limits of 10.5V to 16.0V.

The error lockout mode can be cleared using Land Rover approved diagnostic equipment, or by disconnecting the battery power supply to the FFBH for a minimum of 10 seconds.