Glow Plug relay (Engine management system)

Glow Plug relay

When the starter switch is turned to position ’II’ the engine control module energises the glow plug relay and illuminates the glow plug warning light in the fascia. The glow plug relay supplies a current from the battery to the glow plugs to assist cold starting by raising the temperature of the compressed air in the cylinder to ignition point.

The length of time the glow plugs will remain operational is dependent upon the initial engine temperature determined by the engine control module from the coolant temperature sensor. Once the glow plugs have operated for their pre-determined time the control unit will remove the supply from the glow plug relay and extinguish the glow plug warning light on the fascia.

If an attempt to start the engine is made before the glow plugs have finished operating the engine control module will remove the supply from the glow plug relay, switching off the glow plugs.

Mass air flow sensor

The mass air flow is determined from the cooling effect of inlet air flowing over a Hot Film sensor. This signal is fed back to the engine control module where it is used to monitor the recirculation of exhaust gases. Increase in the exhaust gas recirculation reduces the amount of intake air being drawn into the system, thereby reducing the cooling effect of Hot Film resistor.

Diagnostic connector

The diagnostic connector is located behind the passenger’s ’A’ post lower trim panel. The diagnostic connector is provided to enable diagnosis via TestBook to be carried out without disturbing the system electrical connections and to allow the engine control modules ability to store certain faults to be utilised.

Engine warning lamp

The engine control module has a built in self-diagnosis function. If a fault is detected the engine warning light in the instrument pack will illuminate, and the control module will implement a back-up facility to enable the system to continue functioning, though at a reduced level of performance. If a serious fault is detected the warning light will illuminate and the engine management system will shut down preventing the car from being started or driven.

The warning lamp will remain illuminated until the starter switch is turned off. If the fault is still present when the starter switch is turned back on the warning light will illuminate. If the fault is not present when the starter switch is turned on, the warning lamp will remain extinguished, but a fault code will be stored in the engine control modules memory.