Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.