The electrical input from your BMW spark plug is the source of the explosion that propels your vehicle down the road as you desire. Without this auto part functioning properly your BMW engine will not achieve the level of performance you would expect from your car. If, as a BMW owner, you decide to inspect your spark plugs there is a word or warning that should be adhered to. The socket to remove the plug should be lined with a rubber grommet. This will help to protect the ceramic portion of the plug. If a crack, even one so small that you cannot see it, develops in this ceramic portion of the plug, a spark will not be generated by that spark plug. Furthermore, to prevent the development of a crack in the ceramic section, if any one of your BMW spark plugs is dropped for any reason it should be replaced. The checking of a spark plug on your BMW is the same as other vehicles. The plug has to be removed and reconnected to the ignition wire. The end of the plug should then be placed on a bare section of metal to establish a ground. When the engine is turned over a sharp blue spark should appear between the electrodes and the end of the plug. If the spark is weak then the ignition system should be checked for a faulty part. There is also a very specific type of spark plug that is required by your vehicle. Variations in types of this part include the depth in which the electrode portion fits into the combustion chamber, the gap from the electrode to the bar along with the amount of spark or heat generated by the plug. If any of these vary from the correct specifications set by the factory, the performance of the engine will be negatively affected.