The invention relates to a method for operating an internal combustion engine, having the steps: (a) during an overrun phase of the internal combustion engine, activating an injector of a first combustion chamber for a predetermined activation time tinj with a predetermined activation voltage Ui=1, (b) measuring a torque variation, (c) determining, from the torque variation, a fuel quantity mi=1 of the fuel injected by the injector during the activation time tinj, (d) varying the activation voltage to a value Ui+1 which differs from Ui, (e) repeating steps (a) to (d) with further incrementation of i until i has reached a preset value N or the internal combustion engine is no longer in the overrun phase, and (f) determining an injector characteristic value of the injector of the first combustion chamber from the fuel quantities m1, m2,..., mN and the activation voltages U1, U2,..., UN.