Failed Ignition Coil
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A failed ignition coil prevents proper spark generation in one or more cylinders, causing the air-fuel mixture to burn incompletely or not at all. This is one of the most common misfire sources in BMW engines. You'll typically see cylinder-specific misfire codes (P0301, P0302, etc.) and rough idle or hesitation, especially under load. The fault can worsen quickly if ignored, potentially damaging the catalytic converter.
What it feels like
A failed coil produces rough, uneven running at idle and noticeable loss of power during acceleration. You may hear a distinct knocking or popping sound from the exhaust as unburned fuel ignites in the catalytic converter. The engine runs noticeably smoother when you stop driving that cylinder (which you can't do intentionally, but the contrast becomes obvious). Fuel economy drops and the check engine light stays on. Some drivers report the car feels like it's "running on three cylinders" if one coil is completely dead.
How to confirm it
- Connect a BMW diagnostic scanner and read the fault codes. Note whether the misfire is confined to one cylinder (P0301 for cylinder 1, P0302 for cylinder 2, etc.) or random across all cylinders. A cylinder-specific code points directly to coil, spark plug, injector, or compression on that cylinder.
- Locate the suspected coil pack and inspect the boot and connector for cracks, oil contamination, or loose seating. Oil in the plug well is common on older BMW engines and weakens coil performance.
- Swap the suspected coil to a different cylinder, clear the codes, and retest. If the misfire code moves to the new cylinder, the coil is at fault. If the code stays on the original cylinder, suspect the spark plug, injector, or mechanical compression loss on that cylinder.
- If the misfire stays with the coil pack, replace it with a new unit, reinstall in the original position, clear codes, and road test. The check engine light should not return if the coil was the root cause.
Parts that fix it
Ignition coils and spark plugs are sold individually or in full kit form. Select the kit that matches your engine code (N55, N52, N20, M54, etc.) to ensure proper fit and performance.
Eldor Ignition Coils & Bosch Spark Plugs Tune-Up Kit - BMW N55 by LAIPZ - $249.35. Complete coil and plug set for N55 engines, fits 3-series, 5-series, and X-series models with that engine code.
Genuine BMW High Power Spark Plug Set 8pcs for X5 X6 E70 E71 F15 F16 by Genuine BMW - $220.49. OEM plug set sized for large displacement engines in E70/E71 X5 and X6, and newer F15/F16 models.
Genuine BMW High Power Spark Plug Set 8pcs for E70 E71 E72 F01 by Genuine BMW - $201.97. Genuine plugs for E70 X5, E71 X6, and F01 7-series with eight-cylinder engines.
Mishimoto Ignition Coil Set - BMW M54/N52/N54/N55/S54 2002+ by Mishimoto - $165.95. Aftermarket coil set covering four common BMW inline-six and eight-cylinder engines across two decades of models.
BMW N20 Ignition Coil and NGK Plug Set for BMW by BMW - $103.51. OEM coil and plug pairing for N20 turbocharged four-cylinder engines used in 2012+ 3-series, 4-series, and 5-series.
POCYBER Ignition Coil Set (6 Pack) - BMW N46/N52/N53/N54/N55 by POCYBER - $85.99. Six-pack coil set for N-series naturally aspirated and turbocharged engines, covers most 2000s and 2010s BMW models.