Reliability of automotive parts has been one of the most interesting fields in the automotive industry. Especially small DC motor was issued because of the increasing adoption for passengers’ safety and convenience. For several years, small DC motors have been studied and some problems of a life test method were found out. The field condition was not considered enough in the old life test method. It also needed a lot of test time. For precise life estimation and accelerated life test, new life test procedure was developed based on measured field condition. First, vibration condition on vehicle and latent force on fan motor shaft were measured and correlated with each other. Second, test condition was decided by obtained data. Finally, life of fan motors was estimated by new life test method in shorter test time.