It is the electrical charge the Mercedes-Benz spark plug produces that ignites the air/fuel mixture in the combustion chamber of your engine. This is one of the lowest cost components on your vehicle, but your Mercedes-Benz will not operate at all without them. There is a spark plug on your engine for each cylinder if it is an internal combustion engine that operates on gasoline. If you have a diesel power Mercedes-Benz, then you will not have any. The spark plugs are the last component in the ignition system; after the wires, distributors (on older models), and the ignition coil. Each one of these components plays a vital part in the generation of the electrical impulse that is necessary for the engine to operate. The differences between the many types of Mercedes-Benz spark plugs include the heat range they operate in, the depth they reach into the combustion chamber and the gap setting that must be maintained. It is this gap setting that is adjustable by the owner of the vehicle. The gap is also what changes as the spark plugs become worn from being used. The gap changes because the electrode becomes worn after being used to generate the electrical discharge so many times, which is the reason the spark plugs on your engine will have to be periodically changed. This process is called a tune-up, and if it does not occur at regular intervals the engine's performance and mileage will be adversely affected since the amount of spark being generated will be insufficient to ignite all of the air to fuel mixture in the combustion chamber. For this reason each Mercedes-Benz vehicle should be scheduled annually for a tune-up which has to include a replacement of these ignition components along with a new air and fuel filter.