Slow O2 Sensor During Catalyst Monitor

NAME OF CODE
Slow O2 Sensor During Catalyst Monitor

WHEN MONITORED
With the engine running. coolant greater than 170° F, open throttle, steady to slightly increasing vehicle speed > 18 MPH < 55 MPH, with a light load on the engine, for a period no less than five minutes.

SET CONDITION
The oxygen sensor signal voltage is switching from below 0.39 volt to above 0.6 volt and back fewer times than required.

THEORY OF OPERATION:
Effective control of exhaust emissions is achieved by an oxygen feedback system. Once the sensor reaches its normal operating temperature of 300-350° C (572-662° F), it generates a voltage inversely proportional to the amount of oxygen in the exhaust. This voltage is used to calculate the fuel injector pulse width, which maintains the optimum 14.7 to 1 air/fuel (A/F) ratio that is required for the catalytic converter to best control exhaust emissions. Response rate is the time required for the sensor to detect changes in the exhaust gas oxygen content; it switches from lean to rich it it is exposed to a richer than optimum A/F mixture, or vice versa. The 02S output voltage ranges from 0 to 1 volt. A good sensor easily generates an output voltage in this range as it is exposed to different oxygen concentrations. To detect a shift in the A/F mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the thresholds.

POSSIBLE CAUSES
- Exhaust leak
- Fuel contamination
- Weak 02 sensor with deteriorated catalyst
- Dirt/moisture/grease inside connector
- Engine mechanical