DTC Parameters

• Engine run time is more than 8 minutes and 50 seconds.
• Engine speed is at idle within -75 RPM to 150 RPM of desired idle speed.
• Engine speed more than 1000 RPM for 35 seconds (A/T) or 45 seconds (M/T) after achieving closed loop.
• Engine has not been at idle for more than 47 seconds. Once off idle, counter resets.
• ECT is 158-257°F (70-125°C).
• IAT is -6-176°F (-21-80°C).
• Calculated converter temperature is 933-1161°F (501-627°C).
• Vehicle speed is less than 3 MPH.
• Calculated airflow is less than 8 grams per second.
• Ignition voltage is more than 9 volts.
• BARO is more than 72 kPa.
• No CMP, CKP, ECT, EVAP, fuel tank pressure, FC relay, fuel injector, fuel trim, HO2S2, IAT, idle speed, knock, MAP, misfire, HO2S1, PCM internal fault, TP or vehicle speed DTCs are set.

DTC sets when PCM has determined catalyst to be inefficient by using HO2S2 and HO2S1 signals.

DTC P0420 diagnostic is sampled once at idle once the above conditions have been met. If that test fails, the PCM will take more samples during the current ignition cycle or may take more samples up to six ignition cycles. The extra sampling is to ensure that a converter has truly failed.