P0420

DTC P0420: Catalyst System Efficiency below Threshold

System / Wiring Diagram










Circuit Description

ECM monitors oxygen concentration in the exhaust gas which has passed the three way catalytic converter by HO2S-2.

When the catalyst is functioning properly, the variation cycle of HO2S-2 output voltage (oxygen concentration) is slower than that of HO2S-1 output voltage because of the amount of oxygen in the exhaust gas which has been stored in warm up three way catalytic converter and three way catalytic converter.

Reference

Oscilloscope Waveforms





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.: Between -14 °C and 70 °C (6.8 °F and 158 °F)
- Altitude (barometric pressure): 2020 m, 6650 ft or less (540 mmHg, 72 kPa or more)

1) Connect scan tool to DLC with ignition switch turned OFF.
2) Turn ON ignition switch and clear DTC using scan tool.
3) Increase vehicle speed to 50 - 60 mph, 80 - 100 km/h. (engine speed: 2500 - 3000 r/min.)
4) Keep the vehicle speed for 10 min. or more (Throttle valve opening is kept constant in this step).
5) Stop vehicle and check if DTC / pending DTC exists using scan tool. If not, check if catalyst monitoring test has completed using scan tool. If not in both of the checks (i.e., no DTC / pending DTC and catalyst monitoring test not completed), check vehicle condition (environmental) and repeat step 3 through 5.

DTC Troubleshooting

1.
Was "Engine System Check" performed?
YES
Go to Step 2.
NO
Go to Engine System Check Engine System Check.

2. Exhaust system visual inspection.

Check exhaust system for leaks, damage and loose connection.

Is it in good condition?
YES
Go to Step 3.
NO
Repair or replace.

3. HO2S-2 output voltage check.

Check output voltage of HO2S-2 referring to P0137 DTC P0137 / P0138: Heated Oxygen Sensor (HO2S) Circuit Low / High Voltage (Bank-1 Sensor-2).

Is check result satisfactory?
YES
Replace both catalyst case and exhaust pipe No.1 with new ones.
NO
Check "WHT" and "ORN" wires for open and short, and connections for poor connection.
If wires and connections are OK, replace HO2S-2.

NOTE:

Parts, catalyst case and exhaust pipe No.1, include warm up three way catalytic converter (WU-TWC) and three way catalytic converter (TWC), respectively.