LR3/Disco 3
Junction Box (BJB). The individual glow plugs are grounded through their fixing in the cylinder head. Operation of the
glow plug relays is controlled by the Engine Control Module (ECM), which also controls the illumination of the glow plug
indicator in the instrument cluster.
Each glow plug is a tubular heating element which contains a spiral filament encased in magnesium oxide powder. At the
tip of the tubular heating element is the heater coil. Behind the heater coil, and connected in series, is a control coil. The
control coil regulates the current to the heater coil to ensure that it does not overheat.
SYSTEM OPERATION
There are three phases of glow plug heating: Pre heating, crank heating and post heating. The ECM determines the
heating times from the Engine Coolant Temperature (ECT). The lower the ECT, the longer the heating times.
When the ignition switch is turned to position II, the ECM calculates any required heating times and, if heating is required,
energizes the glow plug relays in the BJB. When pre heating is required, the ECM also sends a message to the
instrument cluster, on the high speed CAN bus, to request illumination of the glow plug indicator. The glow plug indicator
remains illuminated for the duration of the pre heating phase, or until the ignition switch is turned to the crank position,
whichever occurs first. If required, the ECM keeps the glow plug relays energized during cranking and for the duration of
any post heating phase.
The ECM monitors the drive circuit of the glow plug relays for plausibility of operation, continuity, and short and open
circuits. If a fault is detected, the ECM stores a related fault code and permanently illuminates the glow plug indicator
while the ignition switch is in position II.
GLOW PLUG SYSTEM CONTROL DIAGRAM
NOTE :
A = Hardwired Connections
