Circuit Description

HO2S No. 2 is mounted behind the catalytic converter. This sensor is used to determine the oxygen storage capability of the catalytic converter. Oxygen storage capability is used as a measure of converter condition and its ability to perform its function. Sensor heater is powered by ignition voltage. To determine if sensor heater is functioning, its function can only be tested after what is considered a cold start. PCM will monitor airflow and the time it takes for the sensor to become functional. On a hot restart, the heater function cannot be tested due to the amount of heat stored by the catalytic converter. Also, if airflow after start is too high, sensor will not be tested due to the amount of heat generated by the engine, making it difficult to accurately diagnose a heater malfunction.

DTC will set if HO2S No. 2 voltage does not change by greater than 150 mV after 100-190 seconds (depending on coolant temperature and airflow after start up) when coolant and intake air temperatures are within 50°F (10°C) of each other, average air flow is less than 17 gms/s and test is run once per ignition cycle.