VEHICLE DESCRIPTION: LIGHT DUTY TRUCKS AND CAB CHASSIS EQUIPPED WITH GASOLINE ENGINES AND DUAL FUEL TANKS. THE CARBON STEEL FUEL PRESSURE REGULATOR IN THE FUEL SYSTEM CAN WEAR OUT DURING THE LIFE OF THE VEHICLE. IF THE FUEL PRESSURE REGULATOR MALFUNCTIONS, IT CAN CAUSE HIGH FUEL SYSTEM PRESSURE, WHICH DAMAGES THE FUEL PUMP CHECK VALVE. THIS ALLOWS FUEL TO BE TRANSFERRED FROM ONE TANK TO THE OTHER, POSSIBLY OVERFILLING THE NON-OPERATING TANK, RESULTING IN FUEL OVERFLOW PAST THE FILLER CAP.