Amber light
Glow Plug Light (Diesel)
On a diesel, the coil symbol shows the glow plugs are preheating; if it flashes while driving, there is an engine fault.
Normal risk
Waiting for the light to go out before starting is normal. Flashing while driving needs a check soon.
Short answer · Why does the glow plug light stay on or flash?
When you switch on the ignition of a diesel, the light shows the glow plugs are preheating the cylinders; wait until it goes out, then start. If it flashes while driving, many cars use it to signal an engine management fault, sometimes with reduced power. Have the fault code read soon.
What to do
- Wait before startingStart the engine after the light goes out, especially in cold weather.
- If it flashes, read the codeA flashing coil often signals a fault stored by the engine control unit.
- Check starting in the coldHard starting in winter points to a failed glow plug.
How is the light behaving?
| What you see | What it usually means | What to do |
|---|---|---|
| On for a few seconds at start-up | Preheating before start | Wait until it goes out, then start |
| Flashing | Engine management fault on many diesel cars | Have the fault code read soon |
| Steady | Preheat fault or engine fault, depending on the car | Have it checked |
Possible causes
- Normal preheatingExpected on every cold start.
- Failed glow plugHard starting and smoke on cold starts.
- Glow plug control unitThe relay or control unit failed.
- Engine management faultSensors, fuel pressure or particulate filter faults on some models.
Don't confuse it with
Questions about Glow Plug Light (Diesel)
Can I start before the light goes out?
The engine may start, but harder and with more smoke in the cold. Waiting a few seconds is better for the engine.