On a cold engine, the auto-ignition temperature is not reached as a result of air compression alone, so the engine must be warmed up.
For this purpose, a pin glow plug is screwed into each combustion chamber. The glow plug consists mainly of a body with a heated rod pressed into it. When the spark plug is energized, the heating coil in the rod heats the rod to over 850°C, so that the glow to start time rarely exceeds 5 seconds. When the preglow indicator lamp goes out, the engine can be started. Duration of pre-glow and automatic glow after start (up to 20 seconds) controlled by the DDE control unit via a preheat relay.