Coil : A coil is part of the primary ignition system. The coil on a car takes 12 volts and makes 20,000 or more volts to fire your spark plugs. This high voltage is what creates the spark on your engine to explode gasoline within the engine’s combustion chamber. A faulty coil can create a missfire or no-fire situation for your engine. Driving with a bad tune-up can contribute to a coil failure.