Ignition coil
A part that turns the battery's low voltage into the high voltage a spark plug needs to fire.
In plain English
A gasoline engine lights its fuel with spark plugs, but a car battery only supplies about 12 volts, far too little to make a spark jump. The ignition coil is a small transformer that steps that up to many thousands of volts and sends it to the spark plug at the right moment. Most modern engines have one coil for each cylinder, the chamber where the fuel burns, sitting right on top of its spark plug. When a coil fails, that cylinder gets a weak spark or none at all.
Why it's on your estimate
A shop recommends a new coil when testing shows one is not delivering a proper spark, which causes a misfire, meaning a cylinder fails to fire properly. Signs include a rough or shaky idle, hesitation or loss of power when accelerating, hard starting, worse fuel economy, and a check engine light. Worn spark plugs make coils work harder, so a shop may suggest checking or replacing the plugs at the same time.
How urgent is it?
Fix soon
A car with one weak coil will often still drive, but it runs poorly and should be repaired soon rather than driven on for weeks. It becomes more serious if the check engine light is flashing or the engine is shaking badly, because a misfiring cylinder sends unburned fuel into the exhaust, where it can overheat and ruin the catalytic converter.
Questions to ask the shop
- Which cylinder is misfiring, and what test showed the coil is the cause rather than the spark plug or wiring?
- Do the spark plugs need replacing at the same time?
- Are you recommending one coil or all of them, and why?
Got a long estimate full of terms? A free browser AI like HARPA AI can read the page and explain each line in plain English.