Method for operating an internal combustion engine

An internal combustion engine comprising:

• a three-way catalytic converter with lambda control in an exhaust system branch;
• an NOx sensor with an integrated lambda probe is arranged downstream of the three-way catalytic converter;
• wherein the sensor generates an electrical signal representing a lambda value downstream of the three-way catalytic converter and an NH3 signal representing an NH3 concentration in the exhaust gas;
• and
• a control device modifying operation of the internal combustion engine based on the signals generated by the sensor, the control device programmed to:
• employ an NOx sensor with integrated lambda probe downstream of the three-way catalytic converter;
• monitor a signal of the NOx sensor representing a lambda value downstream of the three-way catalytic converter;
• set a threshold value of the signal and determining a lambda setpoint value upstream of the three-way catalytic converter using a difference between the setpoint value of the signal downstream of the three-way catalytic converter and the measured signal if the measured signal is below the threshold value;
• if the measured signal is above the threshold value, determine the lambda setpoint value upstream of the three-way catalytic converter based on a difference between a NH3 setpoint value of the NOx sensor and a measured NH3 signal of the NOx sensor;
• and
• if the measured NH3 concentration is higher than the NH3 setpoint value, increase the lambda setpoint value upstream of the three-way catalytic converter and, if the measured NH3 concentration is lower than the NH3 setpoint.