Patent ID: 8196390

Claim:
A method of monitoring an exhaust gas after-treatment system of an internal combustion engine with a motor block and an exhaust system including an exhaust gas duct, a catalytic converter, an introduction device, and an ammonia sensor positioned in the exhaust gas duct in a direction of exhaust gas flow after the catalytic convertor, wherein the catalytic converter reduces NO x contained in exhaust gas with the aid of a reduction agent including ammonia or a reagent used to derive ammonia that is injected by the introduction device into the exhaust gas duct, the method comprising: increasing a reduction agent metering rate at defined reference operating points until an intentionally induced ammonia breach of the catalytic convertor is detected by the ammonia sensor; and calculating a momentary maximum ammonia storage capacity of the catalytic convertor from a measure of the increase of the reduction agent metering rate up to the induced ammonia breach and additional operating parameters of the exhaust gas after-treatment system.