The voltage produced by your car’s alternator is not strong enough to activate the spark plugs by itself, so it relies on ignition coils. The coils amplify the alternator’s voltage so it is strong enough to make the spark plugs spark. This ignites the fuel in the engine’s cylinders, which then powers your car. Regular wear and tear, an overheating engine or even a short circuit in your car’s wiring can cause your ignition coils to fail. Common signs of coil failure include oil leaking from around the coils or an engine that stalls or refuses to start. Ignition coils are usually simple to replace. Be sure to check them all, though, because if one needs replacing, others probably do, too.