Oxygen Sensors

System uses Bosch oxygen sensors. Voltage range is 0-800 mV. Pre-cat sensors are mounted on top of the exhaust manifolds. Catalysts are integral with the exhaust manifolds.

The post catalyst O2 sensors monitor the efficiency of the catalyst as a requirement of OBD II. This signal also provides feedback of the pre-catalyst sensors efficiency and can cause the PCM to trim the injection time to correct for slight deviations. If the catalyst is operating efficiently, most of the remaining oxygen in the exhaust gas is burned (lack of O2 constant lean signal). The sensor signal fluctuates slightly in the higher end of the voltage scale. If the post sensor shows excessive fluctuations (which echo the scope pattern of the pre sensor), this indicates that the catalytic converter is not functioning correctly. If the post sensor fluctuations move out of the normal voltage window, this indicates that the pre sensor is not performing properly due to slight deterioration. These systems can also trim the injection time to compensate for this. The constantly changing oxygen sensor input to the PCM is needed to correct the injection time to ensure the ideal air/fuel ratio is maintained.