Ignition coils are key to the efficiency and performance of your BMW. With a faulty coil the spark plug is not burning the air/fuel mixture properly and that can lead to problems anywhere in the engine and exhaust (including catalytic converters and O2 sensors). Problems with one or more coils will cause a fault code, but not always a check engine light. A misfire code may be related to an ignition coil, but could be from other things as well. ometimes, a visual inspection of a coil and coil boot will give an indication of a failure. You can also move coils around to different cylinder banks to see if the misfire code follows a suspect coil. We suggest always having one or two coils on hand to keep as spares.
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