Method and apparatus for monitoring a piezoelectric actuator

The method involves determining (140) a characteristic of the actuator, comparing (150) the determined characteristic with an expected characteristic and identifying a fault in the injector if there is a deviation between the determined and anticipated characteristics. It involves detecting charging values and associated voltage values during a charging process and/or a discharging process. Independent claims are also included for the following: (a) an arrangement for implementing the inventive method (b) and a method monitoring a piezoelectric actuator (c) a computer program for implementing the inventive method (d) a computer program product for implementing the inventive method (e) and a digital storage medium for interaction with a programmable computer system.