Abstract: The present invention relates to a diagnosis apparatus which can plan a maintenance plan, a renewal plan, and the like of a self-propelled vehicle, by detecting a work load in addition to an engine condition. Accordingly, there is provided: engine rotating speed detecting means (11), for detecting a rotating speed N of the engine; fuel injection amount detecting means, for detecting a fuel injection amount q per rotation of the engine; loaded weight detecting means, for detecting the weight W of the loaded material; vehicle speed detecting means (14), for detecting the vehicle speed V; and trigger signal oscillating means (82), for oscillating a trigger signal d per predetermined time period to.

Abstract: It is possible to prevent generation of failure in a dump truck and to diagnose a true cause of failure in a short period of time. Thus the present failure diagnosis method diagnoses an operation and function of at least one of respective devices, such as an engine at a predetermined engine rotational speed, a transmission, respective axles, respective suspensions, hydro-pneumatic systems, and a brake while a vessel body (4) descends after evacuation of a load.