The Hyundai Sonata engine comes in a variety of sizes. In most Sonata engines the process of changing a spark plug is the same, with the exception of the 2.7 liter and 3.5 liter engines. Spark plugs need to be replaced every 75,000 to 100,000 miles.
Turn off the Sonata engine and allow it to cool. This normally takes about 30 minutes.
Raise the hood and locate the spark plug cables along the side of the engine. Spark plug cables are normally 1/4 to 1/2 inch thick and plug directly into the engine.
Grasp the cable by its boot. This is the thicker piece that covers the spark plug or spark plug well. Turn the cable back and forth until the lock releases. Pull back on the cable to remove it. Complete the replacement process for each plug before moving on to the next.
Slide the socket, extension and wrench over the spark plug. Turn the wrench to the left to unscrew and remove the plug from the engine. Spark plug sockets have a cushion inside that grab the end of the plug to hold it in place.
Clean the well and boot with the wire brush. Do not rub hard on the well or boot or it will cause damage. Spray silicon in the boot and on the spark plug threads, so you can easily remove the spark plug the next time.
Insert the socket into the well and gently thread it into the engine. Test the tension with the tester. The tension a spark plug needs varies by plug manufacturer. Check the package to find the correct tension. If you need more tension, tighten the spark plug. For less, loosen or unscrew the plug.
Place the cable back onto the spark plug.
Repeat Steps 2 through 7 for the other plugs. Work your way down one side of the engine and then down the other as you replace or clean the spark plugs.
