We recommend a Major Car Service every 24,000 miles or at least every 24 months. A Major Service is the most comprehensive assessment available for a vehicle, and includes all the checks of a Minor Service plus replacement spark plugs and replacement fuel filters for diesel engines. Major Servicing is important to maintain the long-term working condition of your car. Parts like spark plugs should be replaced every 30,000 miles and should be checked routinely to prevent part failure.