How on-board diagnosis (OBD) works

Is everything alright with the exhaust emissions of the vehicle? The on-board diagnosis system (OBD) ensures the necessary clarity at all times. The operational reliability of all components relevant for the exhaust is monitored constantly by an on-board computer. If a part functions incorrectly or fails, the driver is informed about this immediately by a warning lamp on the dashboard and the error code is stored.

In the case of the three-way catalytic converter the on-board diagnosis is made as a rule by measuring the oxygen storage capacity of the catalytic converter. For this purpose the measuring signals of two lambda sensors - one before and one after the catalytic converter - are compared. The signal ratio is then correlated with the degree of conversion for hydrocarbons.