Ignition Coil Packs: Coil-on-Plug and Coil-Pack Designs

The ignition coil converts the 12V battery voltage into the 20,000-40,000V pulse needed to jump the spark plug gap. On modern engines, each cylinder has its own coil (coil-on-plug). On older or some specific engines, a coil pack with multiple high-tension outputs feeds the cylinders through plug leads.

Failure modes

Internal winding failure (open or shorted secondary). The coil produces no spark, or a weak spark that misses combustion. Symptoms: misfire on that cylinder, fault code for cylinder X.

Insulation breakdown — the high-voltage insulation degrades, spark arcs to ground rather than the plug. Symptoms: misfire under specific conditions (humid weather, hard load), sometimes random misfire.

Why one failure rarely stays alone

Coils on the same engine age together. When one fails on an older engine, the others are usually close. Many garages recommend replacing all coils as a set on engines past 80,000-100,000 miles.

Brand

Bosch is OE on most European applications. Beru covers premium German. Hitachi, Denso for Japanese. NGK has aftermarket coverage. The coil pack form factor varies per engine — match by OE part number.

Find ignition coil packs for your engine on the Ignition Coil Packs collection.