Additional Wiring

For complete wiring diagrams, refer to:

The catalyst monitor uses the signals from both the upstream and downstream O2 sensors to detect aging of the catalyst. As a catalyst ages, it loses some of its oxygen storing capacity. As a result, part of the untreated exhaust gases can break through the catalyst and causes the downstream O2 sensor to deviate from its neutral (Stoichiometric) position. By observing the downstream O2 signal, the degradation level of catalyst can be detected. In general, the higher the downstream O2 sensor state of change value, the more exhaust gas breakthrough and the lower the oxygen storage capacity of the catalytic converter.