5.1.1 Description

The exhaust system consists of two separate branches with one catalytic converter in each bank and each catalyst is monitored independently of the other. The signals of both the up-stream control exhaust gas oxygen sensor and the corresponding down-stream monitoring sensor are used for the diagnosis of the catalyst.

If the catalyst has a good conversion capability then the lambda deviations, which are produced by the feedback control system are smoothed by the oxygen storage capacity of the catalyst.

If the catalyst has reduced conversion capability due to ageing, poisoning or misfire, then the lambda deviations produced in front of the catalyst are also visible after the catalyst. The downstream exhaust gas oxygen sensor measures these post-catalyst lambda deviations.