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Warning lights

Glow plug (coil) light flashing on a diesel

On many diesels the coil symbol doubles as an engine fault warning. A flashing light usually means a stored fault, not necessarily a glow plug.

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Symptoms drivers describe

  • Coil-shaped light flashing after start-up
  • Hard starting when cold or white smoke on start-up
  • Rough idle for the first minute from cold
  • Reduced power in some cases

Possible causes

  • Failed glow plugs or a faulty glow plug relay
  • Fuel pressure or injector faults
  • Boost, EGR or DPF-related fault codes
  • Sensor readings out of range
  • Wiring faults in the glow plug circuit

What you can do

  • Note whether it also starts badly from cold
  • Avoid repeated long cranking, which strains the starter and battery
  • Have the codes read before parts are changed

How we check it in the workshop

We read the stored codes, test each glow plug circuit and relay, and check fuelling data before deciding whether the glow plugs are actually at fault.

Is it safe to keep driving?

Usually driveable, but the underlying fault should be identified before winter makes cold starting worse.

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How we can help

Diesel DiagnosticsModern diesels combine high-pressure fuelling, turbocharging, exhaust gas recirculation and after-treatment. When one part of that system drifts, the symptoms usually show up somewhere else.Read more Car Diagnostics & Fault Finding in IverA warning light tells you something has been detected — not what has failed. We diagnose the vehicle first so the repair that follows is the repair the car actually needs.Read more Injector Diagnostics & Injector-Related RepairsInjector faults imitate a lot of other problems. Testing the injector data before replacing anything avoids fitting expensive parts the engine did not need.Read more

Warning lights

Other symptoms in this group

Battery warning light on while drivingThe red battery symbol is a charging-system warning. The engine is normally running on stored battery power only, which is limited.Read more Engine management light flashingA steady amber light and a flashing one are very different. Flashing normally indicates a misfire severe enough to risk expensive damage.Read more DPF warning light onThe DPF light means soot has built up beyond the level the system is happy with. Whether a drive will clear it depends on why it built up.Read more ABS warning light onWith the ABS light on, the anti-lock function has typically disabled itself. The brakes usually still work, but without anti-lock support in an emergency stop.Read more Brake warning light onThe brake warning light covers several different systems, so the first job is establishing which one has triggered it.Read more Airbag warning light onThe airbag light means the restraint system has logged a fault and may not deploy correctly, so it is worth reading properly rather than clearing.Read more

Want this looked at properly?

Send us your registration and describe the symptoms — we will tell you what the next step is.

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