Glow Plug: Description and Operation

The intake manifold glow plugs are located in the cylinder heads, under the valve covers.

The glow plugs are self-regulating. If the engine oil temperature is above 55°C (131°F), the powertrain control module will bulb-check the WAIT TO START lamp but not energize the glow plug relay.

The powertrain control module protects the glow plugs by energizing them for short durations if the battery voltage is abnormally high.

The glow plug ON time varies from 0-120 seconds depending on battery voltage, engine oil temperature and barometric pressure.

On California vehicles the glow plug monitor system is part of the On-Board Diagnostics II (OBD II) System. The Glow Plug Monitor (GPM) system is designed to find failed glow plugs or failed wiring in the glow plug system.

The GPM system uses a low resistance shunt to conduct current to the left and right bank glow plugs.

Three sensing wires measure the voltage drops across the shunt when the glow plugs are operating. A failure in the glow plug system will set a Diagnostic Trouble Code (DTC).