Glow Plug Light: What It Means on a Diesel Car
Written by Muneeb Rana · Last updated 21 October 2026
Quick answer: On a diesel car, the glow plug light comes on when you turn the key to show the glow plugs are warming the engine; wait for it to go out, then start. If it flashes or stays on while driving, the engine computer has found a fault, such as a glow plug, sensor or engine management issue.
TL;DR
- Colour: Amber/yellow.
- Normal at start-up; flashing or staying on while driving means a fault.
- Fix the cause rather than just clearing the light, and log the repair.
The glow plug light is one of the dashboard warnings drivers search for most. This guide covers what it looks like, what it means, how urgent it is and what to do, in plain English. Your owner's manual has the exact symbol and advice for your car.
What does the glow plug light look like?
| Symbol | A coil or spring shape (a wire coil) |
| Colour | Amber/yellow |
| How urgent | Normal at start-up; flashing or staying on while driving means a fault. |
Warning lights follow a rough traffic-light code: red means a serious problem or safety issue, so stop when it's safe; amber or yellow means something needs attention soon; green or blue is information only. See the full dashboard warning lights guide for every common symbol.
What the glow plug light means
Hard starting on cold mornings is an early sign of worn glow plugs.
Common causes:
- Normal pre-heat at start-up
- A failed glow plug or glow plug relay
- An engine management fault (some cars use this light as a general warning)
- A blocked diesel particulate filter on some models
- Fuel or sensor faults
What to do when the glow plug light comes on
- At start-up, wait for the light to go out before cranking.
- If it flashes while driving, reduce speed and avoid heavy loads.
- Get the fault codes read.
- Replace faulty glow plugs as a set if the shop recommends it.
- Log the repair.
Can you drive with the glow plug light on?
If it's only at start-up, yes. If it flashes while driving, drive gently to a garage; the car may go into limp mode.
If you're not sure, treat it as the more serious case. A tow costs far less than a ruined engine, gearbox or set of brakes. If several warning lights come on at once, that often points to an electrical or charging problem; see the check engine light guide and the battery light page.
How to reset or clear it
Don't just clear the light. Most warning lights go out on their own once the fault is fixed, sometimes after a few drive cycles. Clearing a code with a scanner without fixing the cause only hides the problem until it returns, and it can make an emissions test fail because the car's readiness monitors reset.
Keep a record of warning lights and repairs
Write down the date, odometer reading, what the light looked like, the fault code if you had it read, and what fixed it. If the same light comes back, that history saves diagnosis time and money. In CarO you can log the repair and its cost in the car repair log, and set a follow-up with the service reminder tool. For a routine check that catches problems before a light comes on, use our car maintenance checklist. Related: DPF light and seasonal maintenance guide.
Download CarO free on the App Store or Google Play. Free with ads; optional in-app purchases.
Sources
- The AA: Dashboard warning lights and what they mean: www.theaa.com (accessed 21 October 2026)
- Consumer Reports: What the Dashboard Warning Lights Mean in Your Car: www.consumerreports.org (accessed 21 October 2026)
Disclaimer: CarO and this website give general car-care information, not professional advice. Maintenance intervals and specifications vary by vehicle, so always follow your owner's manual and a qualified mechanic. Mileage and cost figures are estimates; check local tax rules before using any log for deductions.
FAQ
What does the glow plug light mean?
On a diesel car, the glow plug light comes on when you turn the key to show the glow plugs are warming the engine; wait for it to go out, then start.
Is it safe to drive with the glow plug light on?
If it's only at start-up, yes. If it flashes while driving, drive gently to a garage; the car may go into limp mode.
What colour is the glow plug light?
Amber/yellow. Red warnings mean stop when safe, amber means get it checked soon, and green or blue lights are information only.
How do I turn off the glow plug light?
Fix the underlying cause; the light usually goes out by itself, sometimes after a few drive cycles. Clearing the code without a repair only hides the problem.
How much does it cost to fix the glow plug light?
It depends entirely on the cause, from nothing for a loose cap or released parking brake to a major repair. Get the fault diagnosed and ask for an itemized estimate before approving work.
Track this in CarO
CarO is a free car maintenance tracker app for iPhone and Android that keeps a full service history, reminds you about oil changes and inspections by mileage or date, and logs fuel fill-ups with MPG, odometer readings and car expenses for every vehicle you own. Logs are stored in the cloud and can be exported as CSV.
