LR3/Disco 3
The brake switch is located on the brake pedal and is operated by the brake pedal. The switch has a normally open circuit
switch which closes the circuit when the driver has applied the brakes. The switch is connected directly to the ECM and
the ECM also receives a brake light signal on the CAN bus from the ABS module.
The ECM uses the brake signal for the following:
To limit fuelling during braking
To inhibit/cancel Speed control if the brakes are applied.
In the event of a brake switch failure, the following symptoms may be observed:
Speed control inactive
Increased fuel consumption.
GLOW PLUGS
Three glow plugs are located in each of the cylinder heads, on the inlet side. The glow plugs and the glow plug relay are a
vital part of the engine starting strategy. The glow plugs heat the air inside the cylinder during cold starts to assist
combustion. The use of glow plugs helps reduce the amount of additional fuel required on start-up, and consequently
reduces the emission of black smoke. The use of glow plugs also reduces the amount of injection advance required,
which reduces engine noise, particularly when idling with a cold engine.
There are three phases of glow plug activity:
Pre-heat
During crank
Post heat
The main part of the glow plug is a tubular heating element which protrudes into the combustion chamber of the engine.
The heating element 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
heater coil to ensure that it does not overheat.
Pre-heat is the length of time the glow plugs operate prior to engine cranking. The ECM controls the pre-heat time based
on ECT sensor output and battery voltage. If the ECT sensor fails, the ECM will use the IAT sensor value as a default
value. The pre-heat duration is extended if the coolant temperature is low and the battery is not fully charged.
