The coil-shaped light on a diesel normally shows briefly before starting. When it flashes or stays on, here is what it means.
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Normally: the glow plugs are warming the engine, so wait for it to go out before starting. Flashing while driving usually means an engine fault.
What it looks like
A coiled spring shape. Colour: Amber.
Common causes
- Normal pre-heat in cold weather
- A failed glow plug
- Engine sensor fault (on many cars this light doubles as a fault warning)
What to do
- Wait for it to go out before cranking the engine.
- If it flashes while driving, treat it like an engine management light and get a diagnostic check.
Can I keep driving?
Yes if it only shows at start-up.
MOT
Not in itself, but an associated engine fault may be.
Symbols vary slightly between makes. Always check your owner's handbook. General guidance only; if in doubt, call your breakdown provider.
Sources and further reading
Facts checked on 20 October 2026. Spotted an error? Tell us and we will correct it.