Glow Plug System: Description and Operation

Glow Plug Q6 System Components

During cold starts, the heat of compression is absorbed quickly by the cold engine. To ensure complete compression ignition, the air needs to be preheated.

Current is supplied to the glow plugs directly from the glow plug relay which is controlled by the ECM. A temperature sensor is connected to a time circuit in the relay and controls preheating time. The colder the engine temperature, the longer the preheating time. The glow plug light in the instrument cluster is on when the plugs are being heated and turns off when the engine is ready to start.


Preglow

Glow plugs are used to preheat the air. If the temperature is below 9°C (48°F), the glow plugs must preglow. Preglowing raises the engine combustion chamber temperature to an appropriate level for starting. The glow plugs are threaded into the cylinder head so they project into each combustion chamber. A heating element in each plug gets red-hot whenever current is supplied to the plug terminals.

Afterglow

Preglow is followed by the afterglow phase after the engine has started. This reduces engine noise, improves idling quality, and reduces the HC emissions shortly after starting by achieving more efficient combustion.

Afterglow is performed and lasts until one of three conditions is met:
Engine speed reaches 2500 rpm
Approximately 180 seconds have passed
Coolant reaches 60°C (140°F)