303-14C Electronic Engine Controls- 2.7L Diesel: Description And Operation (page 17 of 23)

 
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.