Abstract: A diagnosis system for materials handling vehicles leads service personnel step-by-step through diagnosis and repair of faults within the vehicle. Faults are assigned corresponding event codes so that when a fault is detected, its corresponding event code is displayed. The event codes uniquely identify systems of the vehicle in which faults have occurred by having the event codes for a given vehicle system all start with the same number. Thus, the technician knows from the event code what system needs to be diagnosed/repaired and what tools and probable parts will be needed. The event code is used to access diagnosis information identifying the portion of the vehicle wherein the malfunction has occurred, the components which caused the malfunction and, preferably, provides a pictogram of that portion of the vehicle. The technician advances to the malfunctioning portion of the vehicle where another pictorial depiction of the components of that portion of the vehicle assists in locating the components.