Methods comprising: arranging a binary lambda sensor and a second sensor downstream of a catalytic converter; when the engine is run for the first time, using an initial lambda setpoint for closed-loop control; measuring the NH3 value in the exhaust gas; simultaneously measuring the signal from the binary lambda sensor; if the NH3 value lies above a first threshold value, reducing the lambda setpoint value of the binary lambda signal until the NH3 value lies below the first threshold value or the binary sensor signal lies below a second threshold value; recording the corresponding binary sensor signal when the NH3 value passes the first threshold value, for binary sensor signal setpoint value adaptation, as Vbinary-left; and calculating the real lambda setpoint value.