As far as any part for a Mercedes goes, it is best to ask a certified Mercedes or Bosche service professional. Now, with a basic knowledge of engines, one can determine if a part is good or bad. If it is controlled by mechanical ability, then you must check it for mechanical function. If it is electronic, then you must check it electrically. In this case most of todays modern mechanical wounders are contolled by the amount of ohms of resistance that a certain part requires to function properly. Ask your local dealers shop for the specifications of your part. I hope this helps. Hotrodcollingham
