Car encyclopedia

Spark Plug Replacement

Spark plugs wear over time, during normal engine operation, and require periodic replacement

Why Should It Be Serviced?

A worn spark plug may affect engine performance, so it's important to have it serviced. If you don't, you may experience one or more of these symptoms:

  • Check Engine Light may come on or blink
  • Engine may run roughly
  • Abnormal engine noise

When Should It Be Serviced?

  • The spark plugs should be replaced at scheduled intervals, which vary among the car models. Most older vehicles recommend replacement every 30,000 miles; most newer ones have extended this interval to 100,000 miles. Having the spark plugs replaced at the recommended intervals will help reduce the chance of any related drivability concerns.

How It's Done

The technician will remove each ignition wire or individual ignition coil to gain access to each spark plug. The ignition coil(s) and spark plug wires should be thoroughly inspected at this time and replaced an necessary. When the spark plug is completely free of its threads, he or she will lift it out of its spark plug hole and insert the new one. Care should be taken when removing and installing spark plugs to avoid damaging the threads in the cylinder head.

Caution: On vehicles with extended life spark plugs that have spark plug wires, it is often recommended to replace the spark plug wires at the same time the spark plugs are replaced. This is because it can be very difficult to remove the spark plug wires from the spark plugs without damaging the wires. Even if the wires look OK after they are removed, they may be damaged internally. This internal damage can result in an engine misfire with in a few thousand miles of the spark plug replacement.

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