Modern petrol engines depend on the ignition coil to transform the battery's 12 volts into the high-voltage pulse needed to fire the spark plug across its electrode gap. Each coil — whether shared across all cylinders via a distributor cap or dedicated per-cylinder in a coil-on-plug arrangement — must deliver its energy at precisely the right moment for complete combustion. When a coil weakens or fails entirely, the result is a misfire: the affected cylinder stops contributing, the engine vibrates noticeably at idle, fuel consumption climbs, and the diagnostic system typically flags a P0300-series fault code. The coil pack is particularly prone to heat-soak damage after repeated short journeys where the engine bay never fully cools, and older rubber-insulated secondary windings can crack with age. Replacing a failing unit with one that carries the correct OE reference guarantees the output voltage, dwell timing, and connector pinout match exactly what the engine management expects. Bosch and Delphi supply a significant share of original-equipment coils across European marques and their aftermarket units are direct-fit replacements. On coil-on-plug engines it is common practice to replace all coils at the same service interval to prevent cascade failures.
OE coil numbers are specific to the engine code, not just the model range. Two cars from the same year with different displacement or fuel-injection variants often use completely different coils with different connector housings. Use the make-model-engine selector on this page to filter to your exact engine code, then cross-reference the OE number shown against any number printed or moulded on your existing coil. A mismatch in connector pinout can mean the coil fits physically but outputs incorrect voltage at the wrong dwell angle.
On distributor-based systems, a single coil serves all cylinders and must be replaced on its own. On coil-on-plug or coil-pack engines, individual coils can be swapped one at a time, which is fine as a diagnostic repair. However, if one coil has failed due to age or heat damage, the remaining units are likely at a similar stage of wear. Most workshops recommend replacing all coils together when one fails on a high-mileage engine, as it avoids repeat diagnostic visits over the following months.
OEM coils — made by suppliers like Bosch or Delphi — are wound to precise inductance and resistance specifications and pass the vehicle manufacturer's validation testing. Reputable aftermarket coils from Mobiletron or HELLA meet the same electrical parameters and typically carry warranty coverage. Very cheap unbranded coils sometimes use thinner wire windings that overheat and fail prematurely, particularly on turbocharged engines where underbonnet temperatures are higher. Matching the OE number ensures the winding specification is correct regardless of brand.
A rough idle or engine shake that smooths out once revs rise above 1,500 rpm is one of the clearest signs, because a misfiring cylinder is proportionally less disruptive at higher speed. Other symptoms include a check-engine light with a cylinder-specific misfire code, an engine that hesitates or stumbles during acceleration, noticeably increased fuel consumption, and occasionally a smell of unburnt petrol at the exhaust. On cold mornings, a weak coil may cause the engine to start and then stall before the cabin heats up.
Showing 100 of 13,816 Ignition Coil OE numbers. Enter the OE on the main OE search to jump to any reference.
