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
The glow plug provides a heat source for combustion to improve cold engine starting and operation. The glow plugs are made of a resistive material that heats up when electricity flows through it. The glow plugs are duty cycle controlled by the glow plug control module (GPCM) and activated when modulated voltage is supplied. The metallic instant start glow plugs can operate up to 8 minutes (Transit). The ceramic instant start glow plugs can operate up to 20 minutes (all others). The GPCM may activate the glow plugs during an extended idle at cold ambient temperatures. The GPCM provides battery voltage for approximately 2 seconds to heat the glow plugs, then modulates the voltage to 7 volts to maintain temperature. For additional information on glow plug system operation, refer to POWERTRAIN CONTROL HARDWARE Glow Plug Control Module (GPCM).
Typical Glow Plug
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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.