Glow plug control

Glow plug control

The glow plug control unit receives a permanent supply from the battery on the N wire and battery voltage when the starter switch is in position II to ensure continuous glow plug operation during engine cranking from fuse 1 in the passenger compartment fuse box on the W wire. Earth is on the B wire.

When the starter switch is turned to position ’III’(engine crank), battery voltage is switched from the starter switch to the control unit on the W/R wire.

The control unit now connects battery supply to the glow plugs on the N/G wire and the glow plugs start to operate, finding an earth path through the engine. The control unit also provides a supply to the instrument pack on the W/S wire to illuminate the glow plug warning light. The amount of time the glow plug warning light remains illuminated is dependent on under bonnet temperature, which is monitored by a sensor located in the control unit. The engine can be started when the light extinguishes providing the conditions for starting are correct, see Starting.

NOTE: The glow plugs will remain on.

The length of time the control unit will maintain the battery supply to the glow plugs is dependent on glow plug resistance, which increases with temperature and the under bonnet temperature. After cranking the control unit will maintain the supply from the battery to the glow plugs on the N/G wire to give a post heat period for at least 10 seconds. The glow plugs supply is removed automatically by the control unit, either at a temperature of 50oC or after 30 seconds.

Starting

When the starter switch is turned to position ’III’, battery voltage is switched from the starter switch to one side of the starter relay coil on the W/R wire and simultaneously to the glow plug control unit. The other side of the starter relay coil is connected directly to earth for vehicles not fitted with immobilisation. On vehicles fitted with immobilisation, under the correct operating conditions, the immobiliser relay will supply an earth to the other side of the starter relay coil. When the earth is applied, the starter relay is energised.