For commercial vehicles the availability of the truck has become increasingly important to the owner. Unexpected stops and visits to workshops are expensive nuisances not least if caused by some minor faults. The cab comfort and the vehicle response are fundamental to the driver. The accessibility and fault localizing are principal to the mechanic. The safety and the environmental impact are scrutinized by the authorities. The adaptability are vital to the dealers. The climate capability is needed to global presence and to long distance transports. Light weight structural solution permits heavy pay-loads. Low total usage cost is a must to be competitive. Advanced technology is implemented into the truck at increasing rate to satisfy all the aspects above. Quality has become the key issue to reach for the high standard demanded.Due to the growing complexity some ten years ago at Volvo the question was raised whether the ordinary test methods were satisfactory to ascertain acceptable reliability when introducing new and refined models. Systematic and continuous comparisons between test results and the outcome from customer vehicles enhanced the need to introduce additional test activities. As a result reliability tests on proving ground and on remote areas of extreme climate were developed. The reliability tests resemble ordinary customer use. They are comprehensive and deal with all aspects of vehicle usage looked upon with the eyes of the owners, the drivers and the mechanics.The main purpose of the reliability tests is to reveal all quality problems so that they can be corrected before introduction of a new model. All major specifications also in extreme climate circumstances must be covered. The tests must give reproducible results to be used to govern the development and to show the continuous improvement in quality. They can confirm that set goals are met at intermediate and at final stages. The reliability tests have been included in the regular product development process at Volvo Cars and Trucks. They contribute to improved quality and reduced total costs.