A method for checking the functionality of at least one injector (10) of an internal combustion engine (8), in which at least the functionality of a lambda sensor (12), which is designed to ascertain a state of the at least one injector (10) is checked, a steady-state operating condition of the internal combustion engine (8) being set, and a check being performed as to whether at least one signal of the lambda sensor (12) is stable for the set operating condition. Depending on whether the signal of the lambda sensor (12) is stable, a lambda value for the at least one injection valve (10) is measured using the lambda sensor (12) at the set operating condition.