What Is a Ignition Coilpacks?
A coilpack — also called an ignition coil — is an electromagnetic device that transforms the 12-volt supply from the vehicle battery into the 20,000 to 45,000 volts needed to produce a spark across the spark plug gap. Modern engines use individual coilpacks — one per cylinder — in a coil-on-plug configuration, eliminating the need for distributor caps and HT leads. Each coilpack is controlled by the engine management ECU.
What Does the Ignition Coilpacks Do?
The coilpack is the high-voltage transformer in the ignition system. Without a functioning coilpack, the corresponding cylinder cannot fire. Modern coil-on-plug systems allow the ECU to precisely control spark timing independently for each cylinder, optimising combustion efficiency, performance and emissions. Failed coilpacks are one of the most common causes of engine management lights and cylinder misfire fault codes.
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A failed coilpack causes the corresponding cylinder to stop firing — producing a misfire that is usually felt as a rough idle, hesitation under acceleration, loss of power and increased fuel consumption. The engine management light will typically illuminate with a cylinder-specific misfire code (P0300-P0308). In some cases the misfire is only noticeable at idle and clears at higher RPM.
When Should the Ignition Coilpacks Be Replaced?
Coilpacks do not have a fixed service interval — they are replaced on failure. However, worn spark plugs are the single biggest cause of premature coilpack failure, as the coil must work harder to fire across a worn plug gap. Always replace spark plugs at the same time as coilpacks. Individual coilpack replacement costs between £30 and £100 depending on the vehicle.
If you are experiencing symptoms related to your ignition coilpacks and are unsure whether it needs replacing, a free MotorLoom fault scan can help identify whether the component is likely at fault - giving you the most likely cause and estimated repair cost before you visit a garage.
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Related Parts
Other components that work alongside or are related to the ignition coilpacks: