The wheeled tractors that are widely used in various branches of the national economy have a superior design. Various types of faults affect the efficiency of work, increase emissions of hazardous substances and fuel consumption, and affect the safety level and the dynamics of the vehicle. To ensure the appropriate and timely location and repair of faults it is necessary to employ complex diagnostic systems. The study outlines the design of a device used in the diagnostics of the condition of a wheeled tractor. Also, examples of diagnostic algorithms and procedures are also presented. The diagnostic system for the wheeled tractor presented herein considerably improves the reliability of the vehicle and limits the consequences of potential defects. The operator of the tractor is notified immediately after the occurrence of a fault, which prevents further damage to other components of the vehicle and reduces the operating costs. The study also presents the results of tests of the diagnostic facility for wheeled tractors. The results of the tests of the unit were additionally verified by using other diagnostic methods, e.g. with the use of a thermal imaging camera.