Spark plugs ignite the compressed air/fuel mixture in each cylinder of a gasoline engine.
High-voltage current from the coil jumps the plug gap, creating a spark that ignites the mixture at precisely the right crank angle.
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Replacement runs $80–$450 including parts and 0.5-3 hours labor. Exact cost depends on vehicle, parts tier (OEM vs aftermarket), and local labor rate.
Expected lifespan is Copper 20k-30k mi; platinum 60k-80k mi; iridium 100k-120k mi. Driving conditions, climate, and maintenance affect real-world life.
Rough idle; Misfire codes (P0300-P0308); Hard starts; Drop in fuel economy; Hesitation under load; Flashing check-engine light.
Most modern spark plugss are sealed units that get replaced rather than rebuilt. A shop will diagnose, confirm with a load or output test, then swap the unit and verify operation.
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