Tractors represent heavy investment for the farmers, therefore it is very important to avoid severe breakdown and high fixing costs. Regular maintenance and surveillance of the adjustements of the engine are a good way to reduce these costs. Forthree years we have been working on the means of helping the repairers and mark agents in this task. We first realized the expert system SCORPIO 10, which is dedicated to our experimental measure-bench and gives a diagnosis based on the result of a test. We now present an automated diagnosis-bench (BED) that consists of a simple and accurate testing-bench which goes with a system that drives.