Symptoms
- Coil-shaped glow plug icon lit during startup (normal) or staying on/flashing while driving (fault)
- Possible hard starting in cold weather
- May run rough briefly after a cold start if plugs are failing
Likely causes
- CommonNormal preheat cycle before startingThe light is supposed to come on briefly and go off before you start the engine in cold weather.
- CommonOne or more glow plugs failingPlugs wear out individually over time, especially in cold climates.
- PossibleGlow plug relay or control module faultCan prevent all plugs from heating properly even if the plugs themselves are fine.
- PossibleRelated emissions or engine management faultOn some vehicles this same light doubles as a general fault indicator.
What to do
- If the light comes on briefly before starting and goes off, that's normal operation.
- If it stays on after starting or flashes while driving, note any hard-starting or rough-running symptoms.
- Pay attention to cold-start difficulty, especially in winter, which points to failing glow plugs.
- Have the code read at a shop if the light stays on or flashes during driving.
- Replace failed glow plugs as a set if one has failed, since others are usually close behind.
- Have the glow plug relay tested if all plugs check out fine but starting is still difficult.
Tools and parts
Diesel glow plugs (set)Search: “glow plugs for your diesel car make and model”
When to call a pro
See a diesel specialist if cold starts get progressively harder or the light stays on/flashes during driving.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.