COMPONENT INSPECTION Monitor the Catalyst Converter Clear DTC. Start the engine and warm it up until the radiator fan comes on (More than at least 10 minutes ). Drive at a steady speed between 45-55 mph (72-88 km/h) for 30 seconds . Stop and then maintain idle state for 120 seconds in D-position. Repeat step 3 once again. Stop and then keep it in idle state (D-position) for 120 seconds . Repeat step 3 once again. Stop and then maintain idle state for 120 seconds in D-position. IG "OFF" Repeat steps 3 through 9 three times. Check if catalyst monitoring readiness is complete. so, if the readiness is incomplete, repeat steps 2 through 10. Does the scan tool show DTC P0420? YES - Substitute with a known - good Catalyst Converter and check the signal waveform of HO2S for proper operation. If the problem is corrected, Go to "Verification of Vehicle Repair" procedure.