Method to monitor a secondary air system relating to the exhaust gas system of a motor vehicle.

摘要

The invention relates to a method for monitoring a secondary air system connected to the exhaust system of a motor vehicle and to an apparatus for carrying out the method. In the method according to the invention, a first variable, which describes the flow of secondary air injected into the exhaust duct (104) of the internal combustion engine (100) by the secondary air system, is determined. This first variable is used to assess the ability to function of the secondary air system. If the first variable is within a predeterminable interval, the conclusion drawn is that the secondary air system is operating properly. If, on the other hand, the first variable is outside this predeterminable interval, the conclusion is drawn that there is a fault. The first variable is determined from a second variable which describes the air flow fed to the internal combustion engine (100), from the air/fuel ratio in the mixture drawn in by the internal combustion engine (100) and from the air/fuel ratio pertaining in the exhaust duct (104) downstream of the entry of the secondary airline (118).