One of the most-repaired parts for a KitchenAid mixer is called the worm gear. Specific troubleshooting for other repairs can be done directly through KitchenAid's official website because replacement parts may vary depending on usage.
To determine if the worm gear is the part that needs to be replaced, the mixer no longer spins. The worm gear is a piece of hard nylon that helps the mixer process the high levels of friction that the metal gears exert during use. Because of this, the hard nylon eventually wears down and causes the mixer to stop. It is an easily replaceable part and should always be checked first before performing more advanced troubleshooting.
Other common causes for KitchenAid mixer malfunctions are not a direct result of a part needing repair. Instead, a part may just need refilled or adjusted. The two most common repairs in this category are refilling the mixer grease and adjusting the mixer bowl height. Mixer grease occasionally can leak from or clog up the mixer's gear box. Refilling is as simple as opening the gear box, removing any old grease and refilling with new mixer grease. This helps keep all the main parts of the mixer working efficiently. Adjusting the height of the bowl can be done through adjusting the screw under the gearbox. This adjustment can fix a beater from striking the side of the mixing bowl while in use.