There are two sets of windings inside each ignition coil. The primary windings have hundreds of turns of heavy wire, while the secondary side contains thousands of turns of fine wire.  Power supplied by the battery flows through the primary windings. When your car’s computer decides it’s time to fire that cylinder’s spark plug (or plugs), it cuts the current to the primary windings, causing the energy in them to collapse into the secondary windings. This multiplies the voltage, which is then sent to the spark plug in order to make it fire.

Oil or coolant leaks can damage ignition coils—the leaks need to be repaired along with the ignition coil.

Failing ignition coils can cause the engine to run roughly or a lack of power upon acceleration.The Check Engine Light will often flash when the engine is misfiring—continuing to drive under these conditions can damage the catalytic converter.