Fuel pump apparatus

The arrangement has a pump element, a pressure damper with a vent line for compensating fluctuations on the low pressure input side and a shut-off valve in the vent line, whose end not connected to the pressure damper is connected to the clean air side of the engine's induction tube. A diagnostic device detects a pressure damper fault if times at which a lambda probe detects an over-rich mixture are related to shut-off valve opening times. The arrangement (200) has a pump element (210) for delivering fuel from a tank and a pressure damper (240) with a vent line (243) for compensating fluctuations on the low pressure input side of the pump element. A shut-off valve (245) controlled by a controller (250) is fitted in the vent line, whose end not connected to the pressure damper is connected to the clean air side of the engine's (400) induction tube (410). A diagnostic device (260) detects a pressure damper fault if the times at which a lambda probe detects an excessively rich mixture is related to the shut-off valve opening times. AN Independent claim is also included for the following: (a) a method of operating a diagnostic device for a fuel pump arrangement (b) and a computer program for a diagnostic device.