Method for testing an exhaust gas recirculation system

Process for monitoring an exhaust gas in a recirculating device of an I.C. engine comprises adjusting a determined change of the exhaust gas recirculating rate; measuring the NOx concentration in the exhaust gas; and establishing a defect in the recirculating device from the concentration difference depending on the change of the exhaust gas recirculating rate. Preferred Features: The concentration difference from the NOx concentration measured before and after the change of the exhaust gas recirculating rate. The NOx concentration is measured downstream of a NOx storage catalyst and the catalyst is saturated to its maximum storage capability before adjusting the determined change of the exhaust gas recirculating rate. Saturation is recognized downstream of the catalyst. Monitoring is only carried out when the operating parameters of the engine lie within a determined region and/or have limited dynamics.