The PCM/ECM calculates oscillation size of rear HO2S signal which represents catalyst conversion properties. This oscillation size will determine if catalyst conversion is low due to aging or poisoning from leaded fuel or misfiring. The PCM/ECM sets P0420 if the average of calculated oscillation size of rear HO2S signal during predetermined duration is higher than the predetermined threshold.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Check catalyst oxygen storage capacity by evaluating downstream O2 sensor fluctuations | 1. Exhaust gas leaks 2. Faulty rear HO2S 3. Faulty three way catalyst converter |
Enable Conditions |
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Coolant temperature >74℃(165℉)
•
1022℉ < Modeled catalyst temp < 1526℉
•
Vehicle speed >3mph
•
1300< Engine speed <3200
•
0.3g/rev.< MAF <0.9g/rev.
•
Ambient pressure >70kPa(700hPa)
•
Canister load < 0.5
•
Lambda control active & Stable driving condition
•
Downstream O2 sensor operative readiness
•
No opening / closing of Canister Purge Valve
•
No relevant failure
•
11V < Battery voltage < 16V | |
Threshold Value |
•
Average malfunction index > 1 | |
Diagnostic Time |
•
50 Lambda Controller Cycles | |
MIL On Condition |
•
2 Drive Cycles |
