Normal Glow Plug Circuit Operation

A normal functioning system should operate as follows:

1) With ignition switch in the ON position, engine not running and at room temperature, glow plugs are on for 4-to-6 seconds, then off for about 4.5 seconds. Following this on and off cycle, glow plugs are on for about 1.5 seconds and off for about 4.5 seconds. The glow plugs continue to cycle on-and-off in this time sequence for about 20 seconds.

2) If engine is cranked during or after the above sequence, glow plugs will cycle on and off for a total duration of 25 seconds after the ignition switch is returned from the crank position, whether engine starts or not. Engine does not have to be running to terminate glow plug cycling.