Auto Ignition Coil Troubleshooting

Your car's ignition coil transforms the battery's 12-volt output into high voltage electricity that can reach and ignite your engine's spark plugs. These small electrical transformers are found in every gasoline-powered internal combustion engine vehicle and are based on the principles of Faraday's law of induction.

Ignition coils are made of copper windings wrapped around an iron core and embedded in insulating resin. A faulty ignition coil can generate an opening induction voltage that's much higher than the primary coil's voltage, which will result in high-voltage current flowing into the secondary winding and a magnetic field collapsing across the spark plug's gap. This creates a large spark that causes the fuel to ignite and burn.

The current that passes through the primary coil induces a voltage into the secondary coil that's up to 40 kilovolts (20,000 volts). It takes the car's ignition system several components, including a distributor and spark plug wires, to deliver the high-voltage energy to the spark plug. The spark plug then uses the electricity to ignite the air/fuel mixture in the cylinder.

Modern vehicles usually use multiple-coil-pack ignition systems, but the individual coils can still fail causing your engine to misfire. The spark plug in a misfiring cylinder does not fire at the correct time or at all, which leads to unburned fuel leaking into your exhaust system. This wastes your fuel and can cause other problems with your engine and emissions control devices like your catalytic converters.

Most auto mechanics agree that a bad ignition coil is the most common reason for an engine to misfire. The symptoms can be varied, but they include a difficulty starting in cold weather or first thing in the morning, a lack of power, an increased thirst for gas and even the smell of unburned fuel.

A faulty ignition coil may develop cracks in its insulating coating. Moisture can then get into the coil and short out its windings, which causes a failure. This can happen slowly or suddenly, depending on the temperature and vibration of the engine bay.

A faulty ignition coil can also develop a resistance that prevents the flow of current. This also causes a malfunction, which is why it's important to replace the ignition coil as soon as you notice any signs of failure. The good news is that replacing an ignition coil is relatively easy, especially on newer vehicles. The coils are usually located in an accessible spot on the top of your engine and can be removed with a basic socket wrench. Enter your year, make and model to find the right replacement ignition coil for your car or truck.