Glow Plug Light Flashing on a Diesel: What It Means
Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent
A glow plug light flashing on a diesel means the car has found a fault. On some cars that fault is in the glow plug system itself, but on others the flashing light is used to warn of an engine management fault. Either way, it needs a diagnostic check soon, and you should stop driving if the car loses power, runs badly or smokes heavily.
What the glow plug light normally does
Your handbook shows the exact glow plug symbol and colour for your car.
Glow plugs heat up the inside of the engine so a diesel starts easily from cold. When you turn the ignition on, the light comes on for a short time while they heat. Stoneacre explains that the light shows solid while the plugs warm up, and that you should wait for it to go out before starting, especially in cold weather.
So a steady light for a few seconds at start-up is normal. We Buy Any Car notes it may stay on slightly longer in winter, as the plugs need more time to heat.
Why the glow plug light flashes
A flashing light is not normal. Its meaning depends on the make and model, which is why your handbook is the first place to look.
On some cars it means an engine management fault. Vehicle technical data publisher Autodata explains this using a 2015 1.6 diesel Skoda Octavia. On that car, the engine management system makes the glow plug lamp flash when it detects a fault. A fault in the pre-heating system itself would make the lamp come on without flashing. In Autodata’s example, the fault was traced to the engine oil pressure switch.
On other cars it points to the glow plug system. Stoneacre treats a flashing light, or one that stays on after the warm-up, as a sign of a glow plug system fault. Possible causes include:
- Worn or burnt-out glow plugs.
- A faulty glow plug control module or relay.
- Damaged or corroded wiring to the plugs.
- A faulty coolant or air temperature sensor, which can confuse the system.
Because the same light can mean such different things, guessing is a poor idea. Reading the fault codes with a diagnostic tool tells you which system has the problem.
Warning light on? We come to you.
Send a photo of the dashboard and your reg. We will tell you if it looks safe to drive and what it needs.
WhatsApp for a free quote Call 07563 350335
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
Is it safe to drive with the glow plug light flashing?
Be cautious. Advice differs between sources. Stoneacre says a glow plug fault will not stop the engine straight away, but that driving on without fixing it is not advisable. We Buy Any Car strongly advises against driving with the light on and suggests calling a breakdown provider if it appears while driving.
Our advice is to get it checked as soon as you can. Stop driving and call for help if:
- The car loses power or will not rev.
- The engine runs very roughly or misfires.
- There is heavy white smoke.
- Another red warning light comes on at the same time, such as the oil pressure light.
If the light flashes because of an engine fault, carrying on can turn a small repair into a bigger one.
Symptoms you may notice alongside the light
If the glow plugs themselves are the problem, Stoneacre lists the signs as hard starting from cold, rough idling, weaker performance and higher emissions. Green Flag also notes that worn glow plugs cause starting problems.
If the flashing light is warning of an engine management fault instead, the symptoms depend on what has failed. That is another reason to read the fault codes rather than guess.
Other amber lights on diesels have their own meanings. See our guides to the engine management light and the DPF light.
What it costs to fix
There is no fixed price, because the cause could be a sensor, a wiring fault, a relay, glow plugs or something else in the engine. Parts prices and labour time also vary a lot between diesel engines.
The cheapest route is a proper diagnosis first. That stops you paying for parts the car did not need.
How we can help
We are a mobile mechanic, so we come to your home or workplace in Aylesham and across East Kent, including Dover, Deal, Sandwich and Canterbury. See all the areas we cover.
- We do fault finding, so we can read the codes, diagnose why your glow plug light is flashing and tell you what it needs.
- We also service diesels, including diesel fuel filter changes.
Labour is £30-£50 per hour depending on the job and how difficult it is. Parts are extra. We agree the price with you on WhatsApp before any work starts.
Frequently asked questions
Is a flashing glow plug light the same as a solid one?
No. A short solid light at start-up is normal. A flashing light means a fault has been detected.
Does a flashing glow plug light always mean bad glow plugs?
No. On some cars the engine management system uses this light to show other engine faults.
Will the light go off on its own?
Even if it does, the fault that caused it may still be there. Get it checked so you know what caused it.
Can I still start the car?
Often yes, but cold starts may be harder. If it will not start or runs badly, do not keep trying to drive it.
Need help? Send a WhatsApp to 07563 350335 with your car’s make and model and we’ll come to you.
Warning light on? We come to you.
Message us on WhatsApp with your reg and postcode for a price before any work starts.
WhatsApp for a free quote Call 07563 350335
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
