The present disclosure relates to internal combustion engines. The teachings thereof may be embodied in methods for determining a state of an injection valve of an internal combustion engine. Some methods may include actuating the piezo actuator in a pulse-width-modulated manner; recording the T on and/or T off switching times of the pulse-width-modulated piezo output stage of the piezo actuator; and evaluating the recorded switching times to derive the state of the injection valve.