Glow plug light on a diesel: wait until it goes out
This light is preheating, not a fault. Wait until it goes out before you start. If it flashes after the engine has started, that is a fault.
Can you keep driving?
Yes, once it has gone out and the engine runs normally.
What the warning actually means
The symbol looks like a coil or a curl. It shows that the glow plugs are warming the combustion chamber, which a diesel needs in cold weather. It is preheating, not a fault. A light that flashes after the engine has started is the one that means something.
Common causes
- Normal preheating in cold weather, which is the usual reason
- A failed glow plug, if the light flashes after starting
- A fault in the preheat relay or its control
What to do now
- Turn the key and wait for the light to go out before starting.
- If the engine starts hard in the cold, try preheating twice in a row.
- If the light flashes after starting, book an inspection.
What people often get wrong
That the light is an error message. It is preheating, and it should appear on every cold morning. Flashing after start is what means something.
When the car must go to a workshop
A flashing preheat light is a stored fault. The car often runs fine, but starting gets worse with every cold morning.
Read next
- DPF light on: drive, do not park
- AdBlue warning light: fill up before it reaches zero
- Battery light on while driving: what it means
- Used car cold start: why you should see the engine start cold
This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.
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