The catalyst’s efficiency is demonstrated by its ability to oxidize CO and hydrocarbon emissions. The Powertrain Control Module (PCM) compares the output signals of the front and rear oxygen sensors to determine whether the output of the rear sensor is beginning to match the output of the front oxygen sensor. Air/fuel mixture compensation keeps the frequency of the front oxygen sensor high due to the changes from rich-to-lean combusition. The catalyst causes the rear oxygen sensor to have a lower frequency. As the catalyst wears, the rear oxygen sensor’s signal trace begins to match the front oxygen sensor’s signal trace. That is because the catalyst becomes saturated with oxygen and cannot use the oxygen to convert hydrocarbon and CO into H₂O and CO₂ with the same efficiency as when it was new. A completely worn catalyst shows a 100% match between the frequency of the front and rear sensors.
If the oxygen storage time for Bank1/2 is lower than threshold , the PCM determines that a fault exists and a DTC is stored. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till 1 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Manipulates Airfuel and stores the times it takes for the pre and post converter oxygen sensors to switch. | ● Leakage in the exhaust system ● Faulty Catalyst Converter ● Faulty HO2S ● Faulty PCM |
Enable Conditions | ● Engine runtime ≥ 580 ● Purge Concentration Learned ● Airflow in range (3~10 g/s) ● Closed throttle ● Coolant temp in range ● Intake air temp in range ● Barometer above 72 kpa ● Max number of test attempts not exceeded ● Closed loop fueling ● Catalyst temperature in range ● Fuel learning in range ● Vehicle speed below 3kph (2mph) ● Auto trans in gear ● Long term fuel correction learned at idle ● Airflow timer reached limit ● Max idle time not exceeded ● Max number tests not complete ● Disabling faults not present | |
Threshold value | ● Oxygen Storage Time ＜ 1.5 sec. for Bank 1 (2 sec. for Bank 2) | |
Diagnosis Time | - | |
MIL On Condition | ● 1 Driving cycle |
