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 amplitude of B1S2 is different from the model value during 60 sec under enable conditions, PCM sets DTC P0420.
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Oxygen storage capacity (Deterioration of Catalytic efficieny) | ● Exhaust system ● B1S2 ● Catalyst converter |
Enable Conditions | ● Engine speed 800∼3000rpm ● Engine load 28.8 ∼65.3 % ● Catalyst temp.(model) 500∼800℃ ● Closed loop control ● There is not misfire. ● There is not malfunction on HO2S / PCSV / ECTS. | |
Threshold Value | ● Amplitude of downstream O2 sensor > 0.3 | |
Diagnostic Time | ● 60 sec | |
MIL ON Condition | ● 2 driving cycle |
※ B1S1 : upstream oxygen sensor / B1S2 : downstream oxygen sensor
