Normal Glow Plug Circuit Operation

WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1992 Pontiac Trans Sport, 1992 Oldsmobile Silhouette, 1992 Oldsmobile Bravada, 1992 GMC Yukon, and 1992 GMC Vandura Special. However, it is still accessible from the selected car via links, so may be relevant.

A normal functioning system should operate as follows:

With ignition switch in the ON position, engine not running and at room temperature, glow plugs are on for 4-6 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.
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.

NOTE: Glow plug on-and-off times vary with engine temperature, system voltage and/or ambient temperature. Lower temperatures cause longer duration of cycling.