Glow Plug Control (Federal Emissions)
Glow plugs are used to improve cold engine starting and to eliminate White smoke. PCM uses Engine Oil Temperature (EOT) sensor and Barometric Pressure (BARO) sensor to determine how long glow plugs will be on. See Fig 1. PCM energizes glow plugs longer if engine is very cold or if barometric pressure is low at high altitudes. An open in glow plug relay circuit will not allow glow plugs to operate. A glow plugs "always on" condition can be caused by a short circuit. Glow plug relay is located on top of engine. See Figure.