Glow Plug System Description

Engine Controls and Fuel - 3.0L LM2 Diesel | Description and Operation | Document ID: 5731648 Glow Plug Operation In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Six glow plugs are used as an aid to starting. Control of the glow plugs is accomplished by the engine control module (ECM). The nominal voltage for the glow plugs is 5.4 volts. When the ignition is turned On, the engine control module (ECM) applies 7.2 V for 2.2 s, then 5.7 V for 0.8 s and then 5.4 V until 1200°C (2192°F) is reached. The maximum voltage of the system is 10 V. While the engine is running the voltage will vary between 4.7 – 10 V when in closed loop control to maintain a glow plug temperature that ranges from 1150° – 1180°C (2102° – 2156°F). The temperature and the power consumption is controlled by the engine control module (ECM) within a wide range to suit the engine’s pre– heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre–glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault. A normal functioning system operates as follows: Turn the ignition On with the engine Off, and at room temperature. The glow plugs turn On and 7.2 V is applied for 2.2 s, then 5.7 V for 0.8 s and then 5.4 V to reach 1200°C (2192°F). The wait to start indicator is ON for 1 second during cold start. The wait to start indicator may not illuminate during a warm engine start. If the engine is cranked during or after the above sequence, the glow plugs may cycle On and Off after the ignition switch is returned from the start position to the run position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling. The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer On times.