What Causes Ignition Coils to Go Bad?

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The top reason ignition coils fail is bad spark plugs or plug wires. Another potential cause is heat and vibration, which can damage the ignition coil's windings and insulation. If an engine is experiencing repeated coil failures, the underlying cause may be resistance from worn spark plugs or excessive spark plug gap. In rare cases, the failure may be due to a lean fuel condition caused by leaky valves.