Glow Plug: Description and Operation

Glow Plugs

The diesel engine glow plugs are threaded into the cylinder head and extend into the combustion prechamber. The purpose of the plugs is to heat air entering the combustion chambers to help start the combustion process when the engine is cold.

The glow plugs are used as an aid to starting; especially when ambient temperatures are low. The plugs are cycled on/off for short time periods prior to engine cranking and during initial start-up. The plugs are not on continuously, as plug damage can occur after 6-7 seconds.

Turbo diesel engines use a glow plug relay that is controlled by the PCM based on inputs from engine temperature sensors. The glow plugs will cycle after the engine has started to maintain good combustion.