Quote:

The auxiliary fuel pump regulates the fuel supply to the FFBH. The pump is installed in a rubber mounting attached to the chassis, below the RH front seat. The pump is a self priming, solenoid operated plunger pump, controlled by a Pulse Width Modulated (PWM) signal from the control module in the FFBH. When the pump is de-energized, it provides a positive shut-off of the fuel supply.

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

The control module is in the lockout mode (see Diagnostics at the end of this section).
A crash message is received from the restraints control module. For additional information, refer to Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS) (501-20B Supplemental Restraint System)
A low fuel level message is received from the instrument cluster. For additional information, refer to Instrument Cluster (413-01 Instrument Cluster)
The battery voltage is too low. When starting the FFBH, battery voltage must be 10.25 - 15.5 volts. When the FFBH is running, operation will be discontinued if battery voltage decreases to less than 10.25 volts.


The control module monitors the FFBH system for faults. Any faults detected are stored in a volatile memory in the control module, which can be interrogated by T4. 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 control module 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 control module immediately stops the auxiliary fuel pump, and stops the combustion air fan and circulation pump after a cool down time of approximately 2 minutes. Error lockout occurs for start sequence failures, combustion flameouts, heat exchanger casing overheat and if battery voltage is out of limits. The error lockout mode can be cleared using T4, or by disconnecting the battery power supply (connector C0926) for a minimum of 10 seconds.

Start Failure and Flameout: If a start sequence fails to establish combustion, or a flameout occurs after combustion is established, the control module immediately initiates another start sequence. The start failure or flameout is also recorded by an event timer in the control module. 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 control module enters the error lockout mode.

Heat Exchanger Casing Overheat: To protect the system from excessive temperatures, the control module enters the error lockout mode if the heat exchanger coolant temperature exceeds 125 °C (257 °F).

DGs quote wrote:

When the pump is de-energized, it provides a positive shut-off of the fuel supply.