What it means
Before starting a diesel engine, it usually means the glow plugs are heating the combustion chambers; wait for the indicator to go out before starting if the manual says to do so. If it stays on or flashes after the engine starts, it can indicate a diesel engine-management fault; colour and exact behaviour vary by manufacturer.
What the symbol looks like: A coil-shaped or looped line, usually shown as an amber dashboard indicator.
Why it comes on
- Normal glow-plug preheating in cold conditions
- One or more failed glow plugs
- Glow-plug control module or relay fault
- Wiring or connector fault
- Engine-management fault indicated by a flashing light
What to do
- With the ignition on, wait for the preheat indicator to go out before starting, as directed by the manual.
- If it remains on or flashes while driving, note any change in engine performance.
- Check the owner's manual for the meaning of a flashing or persistent indicator.
- Arrange a diagnostic check if it persists or the engine is difficult to start.
Can I keep driving?
A normal preheat light that goes out is not a reason to avoid driving. If it stays on or flashes while driving, drive cautiously only if the engine runs normally and arrange a prompt check.
Symbols and colours differ between makes and models. Your owner’s manual shows the exact lights of your car.