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Engine

What is an Ignition Coil?

Turns 12 volts into 30,000+ volts to light the spark plug.

IGNITION COIL — 12V → 30,000V−+12VBATTERYECUtrigger pulseCOIL (cutaway)laminated iron coreB-fieldsecondary~20,000 turnsprimary~200 turnsN₁ : N₂ ≈ 1 : 100SW~30,000 Vspark plugCHARGEFIRE ⚡switch closed → current flows → magnetic field buildsswitch opens → field collapses → 30 kV induced in secondaryFew primary turns × many secondary turns = massive voltage step-up (fires ~50× per second at 3000 rpm)

Simplified animation — not to scale.

In plain English

A small transformer (sometimes one per cylinder) sitting on top of the spark plug. It takes battery voltage and steps it up massively.

A simple analogy

"It is a tiny lightning generator — turns a polite 12-volt nudge into the bolt that lights the fire."

How it works

The ECU triggers the coil, which dumps a huge high-voltage pulse into the spark plug at exactly the right moment to ignite the fuel-air mixture.

Signs of trouble

  • ⚠Misfires, especially under load
  • ⚠Juddering or shaking
  • ⚠Loss of power and bad MPG
  • ⚠Check engine light with misfire codes
Rough UK cost

£70–£300 per coil (petrol only)

Parts: £25–£100 per coil
Labour: £40–£150

Always get a written quote. Prices vary by car, region, and parts brand.

Heads up: Carautonomy is for general guidance only. If your car is showing warning lights or behaving oddly, get it looked at by a qualified mechanic.

Keep exploring

Alternator
The on-board power station that keeps your battery topped up.
EGR Valve
A small valve that recycles exhaust gas to reduce emissions.
Starter Motor
The muscle that turns your engine over when you twist the key.

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A friendly note

Information here is general guidance, not a diagnosis. Always speak to a qualified mechanic before parting with cash.

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