Glow Plug Relay: Description and Operation

GLOW PLUG RELAY/CONTROLLER
The glow plug relay is a solid state device which operates the glow plugs on Federal Emissions Vehicles. The glow plug controller is a solid state device which operates the glow plugs on California Emissions vehicles. Both components perform the same function of turning ON the glow plugs based on ECM commands

The glow plug controller or relay is connected to the following circuits:
- The fuel heater ignition 1 voltage circuit
- The battery voltage circuit
- The glow plug enable circuit located between the ECM and the glow plug relay or controller
- The engine ground circuit
- The glow plug supply voltage circuit located between the glow plug relay/controller and the glow plugs.

On the California Emissions vehicles, the glow plug diagnostic circuit connects directly from the ECM to the glow plug controller. On Federal emissions vehicles, the glow plug diagnostic circuit is spliced to the glow plug enable circuit after the relay.