The Land Rover Discovery 4 Glow Plug Relay Location Official Guide

Land Rover Discovery 4 Glow Plug Relay Location

This guide will help the owner find the Land Rover Discovery 4 glow plug relay location and explain a little about the glow plug system.

The glow plug system has a glow plug installed in the inlet side of each cylinder. The glow plugs heat the combustion chambers before and during cranking, to aid cold starting. After the engine starts to reduce emissions and engine noise when idling with a cold engine. A glow plug wiring harness on each bank of glow plugs is connected to a separate relay and fusible link in the Battery
Junction Box (BJB). The individual glow plugs are grounded through their fixing in the cylinder head.

Engine Control Module

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. The Land Rover Discovery 4 glow plug relay location is shown below at points 1 and 2 on the illustration below.

Land Rover Discovery 4 Glow Plug Relay Location

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.


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If you would like more information on the Land Rover Discovery 4 glow plug location, or any other problem you may have with your Discovery 4. Consider downloading our fully illustrated repair manual. Thousands of pages of text, photos and illustrations that will get your Land Rover back on the road.

LINK : Land Rover Discovery 4 Repair Manual