Ignition Coil
An induction coil that transforms the battery's low voltage into the thousands of volts needed to create an electrical spark in the spark plugs.
An ignition coil (or spark coil) is an essential component of a vehicle's ignition system. It acts as a miniature transformer, converting the vehicle's low 12-volt battery power into the high-voltage electrical current (typically 20,000 to 50,000 volts) required to bridge the gap of a spark plug and ignite the fuel-air mixture.
Modern vehicles use a Coil-on-Plug (COP) design, where a separate individual ignition coil sits directly on top of each spark plug, eliminating the need for spark plug wires and a distributor. Older vehicles used a single ignition coil connected to a distributor that routed the spark to each cylinder in sequence.
Ignition coils can fail due to electrical overload, heat, vibration, or oil leaks from a valve cover gasket soaking the boot. A failing ignition coil will cause one or more cylinders to stop firing properly. Symptoms include engine misfires, a rough idle, engine hesitation or jerking, poor acceleration, a drop in fuel economy, and a check engine light displaying ignition-related codes (such as P0351 through P0358).
Driving with a failed ignition coil can cause unburned fuel to travel into the exhaust system, which will rapidly overheat and destroy the catalytic converter. Replacing a failing coil immediately prevents subsequent, more expensive repairs.