The GMC Sierra is available in 1500 and 2500 models. The spark plug replacement process on both of these GMC Sierra models is the same. GMC suggests that all spark plugs be replaced every 100,000 miles. When removing spark plugs, always remove one spark plug wire at a time to avoid mixing up the wires.
Disconnect the negative battery cable and allow the engine to cool.
Find the spark plugs on the vehicle that are located on the sides of the engine. Some of the GMC Sierra engines have a rubber flap covering the sides. Remove the flap to gain access to the spark plugs.
Take the spark plug wire by the boot and turn it to release the lock. Pull back on the spark plug wire by the boot. This removes the wire from the spark plug revealing the spark plug.
Cover the spark plug with the socket. Use the extension and the socket wrench to unscrew the spark plug. Pull the spark plug out of the cylinder head.
Spray silicone onto the threads of the spark plug and insert the new spark plug into the socket. Use the socket and wrench to thread the new spark plug in place. Gently turn the spark plug to the right to start the threading process. Never force the spark plug into the bore.
Connect the spark plug cable to the end of the spark plug and remove the next spark plug cable. Repeat the above process for the rest of the spark plugs.
Connect the battery cable and replace the rubber flap, if removed in Step 2.
