P0420
DTC P0420: Catalyst System Efficiency below Threshold (Bank 1)Wiring Diagram:
System / Wiring Diagram
Circuit Description
Exhaust oxygen concentration at the pre-catalyst and the post-catalyst of WU-TWC is detected from HO2S-1 and HO2S-2 respectively and accordingly ECM controls the closed loop which then controls the fuel injection volume. While the above control is going on and if WU-TWC is in good condition, the output voltage of HO2S-2 is maintained at specified level. As WU-TWC becomes deteriorated, even when the above control is going on, the exhaust gas which has passed WU-TWC then passes HO2S-2 at the exhaust oxygen concentration similar to that of the pre-catalyst without being oxygenated or converted. Thus, waveforms of HO2S-1 and HO2S-2 output voltages become alike. ECM judges deterioration of WU-TWC by comparing waveforms of HO2S-1 and HO2S-2.
DTC Detecting Condition and Trouble Area
DTC Confirmation Procedure
WARNING:
- When performing a road test, select a place where there is no traffic or possibility of a traffic accident and be very careful during testing to avoid occurrence of an accident.
- Road test should be carried out with 2 persons, a driver and a tester, on a level road.
NOTE: Check to make sure that the following conditions are satisfied when using this DTC Confirmation Procedure.
- Intake air temp.: -8 degrees C (18 degrees F) or higher
- Engine coolant temp.: 74 - 110 degrees C (165 - 230 degrees F)
- Altitude (barometric pressure): 2400 m, 8000 ft or less (560 mmHg (75 kPa) or more)
1. Connect scan tool to DLC with ignition switch turned OFF.
2. Turn ON ignition switch and clear DTC, pending DTC and freeze frame data by using scan tool.
3. Increase vehicle speed to 80 - 90 km/h (50 - 56 mph).
4. Keep above vehicle speed for 5 min. or more (Throttle valve opening is kept constant in this step).
5. Stop vehicle and check if pending DTC exists by using scan tool. If not, check if catalyst monitoring test has completed by using scan tool. If not in both of above checks (i.e., no pending DTC and catalyst monitoring test not completed), check vehicle condition (environmental) and repeat Steps 3) through 5).
Step 1 - 3:
DTC Troubleshooting