Glow plug light flashing on a diesel
A glow plug light flashing on the dash rarely means the glow plugs alone. On many diesels, especially VW Group models, the coil-shaped light doubles as an engine fault warning, often with a sudden drop in power.
The short answer
A flashing glow plug or heater plug light means the ECU has found an engine fault that needs attention. On VW, Audi, Seat and Skoda diesels it's commonly linked to boost, fuel pressure or sensor faults, and the car often goes into limp mode.
You can usually get home or to a safe place gently, but don't keep using the car for long journeys. Book a diagnostic before the fault causes more wear or leaves you stranded.
What the glow plug light normally does
When you turn the key on a cold diesel, the glow plug light comes on while the plugs heat the cylinders, then goes out when the engine is ready to start. On a warm engine it may only flash on for a second.
That solid light at start-up is normal. A light that stays on or flashes with the engine running is a warning.
Solid or flashing
| Light behaviour | What it usually means |
|---|---|
| On briefly at ignition, then out | Normal pre-heating |
| Stays on with the engine running | A glow plug or glow plug control fault on many makes |
| Flashing with the engine running | An engine management fault, often with reduced power, especially on VW Group diesels |
| Flashing with the engine management light on | A fault the ECU rates as serious, see our flashing engine light guide |
Common causes of a flashing coil light
Each of these can make the ECU flash the light and cut power. Only a code read tells you which applies.
Underboost or overboost
A boost leak, sticking turbo vanes or a failing actuator, logged as P0299 or P0234.
Low fuel rail pressure
A blocked fuel filter or weak pump can set P0087 and cause hesitation under load.
DPF and EGR problems
A blocked filter or a sticking EGR valve can bring on the light alongside the DPF or engine light.
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Get in TouchWhat to do when the light starts flashing
Ease off
Avoid hard acceleration and keep the revs low.
Find somewhere safe to stop
Switch off and wait a minute before restarting.
See if the light returns
A restart sometimes restores power until the fault happens again, but the code stays stored.
Write down what happened
Note the speed, load and weather, as this helps pin down intermittent faults.
Book a diagnostic
The codes and live data show whether it's boost, fuel or the glow plug circuit.
Vans with a flashing coil light
VW Transporters, Crafters and Caddys use the same warning system as the cars, so a loaded van climbing a hill is a common moment for the light to start flashing. Boost leaks and sticking turbo vanes show up most under that kind of strain.
We can check vans at your yard or depot, so the fault can be found between jobs.
Can I keep using the car with the glow plug light flashing?
For a short, gentle journey, usually yes. The ECU has limited power to protect the engine, so get the codes read before you use it normally again.
Does a flashing glow plug light mean the glow plugs need replacing?
Not necessarily. On VW Group diesels it's a general engine fault warning. The glow plugs are only to blame if a glow plug code is stored.
Why is the coil light flashing on my VW?
VW uses the coil light to flag engine faults on its TDI engines. Boost leaks, sticking turbo vanes and fuel pressure faults are among the usual causes.
Will the flashing light go out by itself?
It may go out after a restart, but the fault code remains stored. If the cause hasn't been fixed, the light and the power loss tend to come back.
Find out why the coil light is flashing
A mobile diagnostic reads the stored codes and live engine data for £100 + VAT, at your home or workplace. If the cause is a boost leak or a blocked DPF, we can often sort it on the same visit or a follow-up.
Email the codes to sales@sgrautomotive.co.uk if you already have them
Eccles, Manchester M30 0SF