Ignition Coil Service Video

An ignition coil turns your battery's 12 volts into the tens of thousands of volts a spark plug needs to fire. Most modern engines have one coil sitting on top of each spark plug. When a single coil fails, that whole cylinder stops firing.

This video shows what a coil looks like once it is pulled from the engine and what a broken-down boot or winding looks like up close. It also shows how the misfire appears on a scan tool, which explains why one bad coil can shake the whole engine.

Inside the coil, a primary winding builds a magnetic field that collapses into a secondary winding, stepping the voltage up to around 40,000 volts. That charge travels through a rubber boot into the plug and jumps the gap to ignite the fuel. Coil testing is part of our engine diagnostics service, where a misfire is treated as a question to answer before any part is ordered.

Coils usually fail in one of two ways. Heat breaks down the internal windings over time, or the rubber boot cracks and lets the spark jump to the engine instead of the plug.

A rough idle that smooths out at higher RPM is the classic sign. You may also feel a stumble when you accelerate. A check engine light with a P0301 to P0308 code points straight to the cylinder that is misfiring.

If the check engine light is flashing, the misfire is severe enough to damage the catalytic converter, so the car should not be driven far. Fuel economy also drops, because unburned fuel is passing into the exhaust.

At Spectra Auto Services, our technicians read the misfire counters and fuel trims before taking anything apart. They move the suspect coil to another cylinder to see whether the misfire follows it, which rules out a fouled plug or a bad injector. You get DVI photos and scan results before any work is approved.

Coils and spark plugs wear together, so a failed coil is often a sign the plugs are due as well. Our tune-up and spark plug replacement service covers both, using OEM coils when one needs replacing.

A cracked coil boot leaks spark worst on cold, damp Frederick County mornings, when moisture gives the high voltage an easier path to ground. Drivers from Mount Airy and Middletown often bring us a shaking idle that turned out to be a single coil.

If your engine shakes at idle or the check engine light is flashing, call Spectra Auto Services at (301) 695-5990, or find car repair near me in Frederick to have the misfire diagnosed.