Ignition Coil

Ignition coils convert your battery's 12 volts into the 20,000–45,000 volts needed to fire the spark plugs. Most modern vehicles use coil-on-plug (COP) or direct ignition coils - one per cylinder - rather than a single distributor coil, meaning a failure affects only one cylinder but will still trigger a misfire code and noticeable performance loss. Coils don't have a fixed replacement interval, but they commonly fail between 80,000–100,000 miles, especially when spark plugs are overdue. Heat, oil leaks onto coil boots, and worn spark plugs that force coils to work harder all accelerate failure. This catalog covers the full range: standard and direct ignition coils, coil boot kits (essential when oil has contaminated the plug well), coil assemblies, and hardware. When buying, match the coil to your exact engine code - not just year, make, and model - since many platforms share body styles across different displacement options with incompatible coil designs. OEM-equivalent units from brands like Delphi, Standard, and Bosch are reliable choices for daily drivers; OEM is worth the premium on high-mileage imports.

Signs you need replacement

• Check engine light with a P030X misfire code - A cylinder-specific misfire code (P0301–P0308) pointing to one cylinder is a strong indicator of a failed coil on that cylinder. Swap the suspect coil with an adjacent one and rescan; if the misfire code follows the coil, replace it.
• Rough idle or engine stumble at low RPM - A misfiring cylinder causes the engine to shake noticeably at idle. It may smooth out at higher RPMs, which can mask the problem, but the misfire is still occurring and will worsen over time.
• Hard starting or extended cranking - If one or more coils are weak rather than fully failed, the engine may crank longer than normal before firing, particularly in cold weather when ignition demands are higher.
• Visible cracks, carbon tracking, or oil contamination on the coil or boot - A cracked coil tower or boot allows voltage to arc to ground instead of reaching the plug. Oil in the plug well soaks into the boot and degrades the coil body; replace the boot kit alongside the coil in this case.
• Fuel smell or poor fuel economy - Unburned fuel from a misfiring cylinder exits through the exhaust and can eventually damage the catalytic converter. A sudden drop in MPG paired with a rough idle warrants immediate coil diagnosis.

Frequently asked questions

• Should I replace all ignition coils at once, or just the one that failed? If your vehicle uses coil-on-plug design and one coil fails after 80,000+ miles, replacing all coils at the same service is worth considering - the remaining coils are the same age and mileage. On vehicles with fewer than 60,000 miles, replacing only the failed coil is reasonable. Always replace spark plugs at the same time.
• Are aftermarket ignition coils as reliable as OEM? Quality varies significantly. Brands like Delphi, Bosch, Standard/Blue Streak, and NGK manufacture to OEM specifications and are appropriate for most applications. Avoid unbranded coils, especially on European vehicles - BMW, Audi, and Mercedes coils are sensitive to voltage and thermal tolerance, where OEM or OEM-equivalent parts pay off.
• What's the typical cost to replace an ignition coil, and is it a DIY job? Individual coils range from $20–$120 depending on vehicle and brand; OEM units for European makes can run $80–$200 each. On most domestic and Japanese vehicles, COP coil replacement is a straightforward DIY job - remove the engine cover, unplug the connector, pull the coil, and swap it. Budget 15–30 minutes per coil with basic hand tools.