Method of checking the functional capability of a catalytic converter

A method of checking a functional capability of a catalytic converter in an exhaust system of a lambda-controlled internal-combustion engine, the method which comprises:

• determining an efficiency value of an efficiency of a catalytic converter by determining an oxygen storage capability of the catalytic converter;
• calculating a substitute value for a temperature in the catalytic converter by continuously adding up a heat supplied to the catalytic converter by an exhaust gas for providing a summation value, the heat supplied to the catalytic converter being dependent on a speed and a load of an internal-combustion engine, and subjecting the summation value to a low-pass filtering and calculating the substitute value from the summation value minus a result of the low-pass filtering;
• adjusting the efficiency value for temperature influences with the substitute value for providing an adjusted efficiency value;
• and
• subsequently obtaining a measure of a functional capability of the catalytic converter from the adjusted efficiency value.