Pre-heating system for diesel engines (Audi A8 D2)

Each swirl chamber has a glow plug. Glow plugs are used when starting a cold engine. The voltage supply to the glow plugs is controlled by a time relay from a signal from the engine ECU.

The indicator lamp in the instrument cluster lights when the glow plugs are operating. After the lamp goes out, the engine can be started. Voltage is supplied to the glow plugs for a few seconds after the indicator lamp comes on. If no attempt is made to start the engine after the lamp goes out, the timer disconnects the voltage from the glow plugs to prevent the battery from discharging and the glow plugs from overheating.