On a cold engine, the auto-ignition temperature is not reached by compression alone, so preheating of the fuel mixture is necessary.
For this purpose, a glow plug is screwed into each combustion chamber. A glow plug basically consists of a body with a heating rod pressed into it. When voltage is applied, the heater winding in the rod heats up to a temperature of over +850°C within a few seconds, due to which the warm-up time before starting rarely lasts more than 10 seconds. When the warm-up indicator lamp on the instrument panel goes out, the engine can be started.
To speed up the heating of the engine, the glow continues even after it is started. The duration of pre-glow is determined by the control unit depending on the temperature of the coolant. The control unit is located behind the center console under the air duct.
Information about the engine temperature enters the control unit from the coolant temperature sensor. Based on the received data, the control unit determines the duration and magnitude of the current.