A non-transitory computer-readable data storage medium storing a computer program having program codes which, when executed on a computer, performs a method for testing a fuel quantity balance in a common rail system of an internal combustion engine having two electrically controllable actuating elements including a first controllable valve at the input side of a high-pressure fuel pump and a second controllable valve on the common rail, the method comprising:
- (a) setting a regulating mode by designating one of the two electrically controllable actuating elements as a controlled actuating element and designating the other electrically controllable actuating element as a regulated actuating element;
- (b) setting a defined operating state of the engine by specifying an engine rotational speed and a rail pressure;
- (c) setting a first system operating point by controlling the controlled actuating element;
- (d) measuring a first current value of one of the two electrically controllable actuating elements;
- (e) setting a second system operating point by controlling the controlled actuating element;
- (f) measuring a second current value of one of the two electrically controllable actuating elements;
- (g) forming a current value difference between the first and second current values;
- (h) performing a comparison between the current value difference and an assigned prespecified value;
- and
- (i) evaluating whether the fuel quantity balance shows an insufficient quantity, based on the result of the comparison.