P0420

DTC P0420

DTC Detecting Condition and Trouble Area






Wiring Diagram










System Description

ECM monitors oxygen concentration in the exhaust gas which has passed the TWC by HO2S. When the catalyst is functioning properly, the variation cycle of HO2S output voltage (oxygen concentration) is slower than that of A/F sensor output signal because the amount of oxygen in the exhaust gas is stored in TWC.

DTC Confirmation Procedure

WARNING:

If you do not select a suitable route and take proper precautions when performing a road test, an accident can occur.

- Select a level road with no traffic to minimize the risk of accident.
- Perform the test extremely carefully.
- Perform the road test using 2 persons, a driver and an assistant.

NOTE:

- If DTCs other than aimed DTC are previously detected in DTC confirmation procedure, be sure to troubleshoot DTC previously detected.
- Check that the following condition is satisfied when using this procedure.

- ECT > 70 °C (158 °F)

1) Warm up engine to normal operating temperature.
2) Drive vehicle at 80 - 100 km/h (50 - 62 mile/h) for 10 min. (Keep throttle valve opening constantly and engine speed at 2,500 - 3,000 rpm in this step.)

DTC Troubleshooting

1.
Was "Engine and Emission Control System Check" performed?
YES -
Go to Step 2.
NO -
Go to Engine and Emission Control System Check Engine and Emission Control System Check.

2. DTC check

Check DTC.

Is there DTC(s) other than P0420?
YES -
Go to troubleshooting for applicable DTC.
NO -
Go to Step 3.

3. Exhaust system visual inspection

Check exhaust system for leak, damage and looseness.

Is it in good condition?
YES -
Go to Step 4.
NO -
Repair or replace defective parts.

4. HO2S circuit check

Check signal and ground circuits of HO2S for high resistance according to step 3 under P0137 DTC P0137 / P0138.

Are they in good condition?
YES -
Go to Step 5.
NO -
Repair or replace defective wire harness.

5. A/F sensor signal circuit check

Check A/F sensor signal circuit according to Step 3 under P0131 DTC P0131 / P0132 / P0134 / P2237.

Are they in good condition?
YES -
Go to Step 6.
NO -
Repair or replace defective wire.

6. Replace exhaust manifold (built in TWC). Exhaust Manifold Removal and Installation
Perform DTC confirmation procedure.

Is DTC P0420 still detected?
YES -
Go to Step 7.
NO -
End.

7. Replace HO2S. Heated Oxygen Sensor (HO2S) Removal and Installation
Check DTC.

Is DTC P0420 still detected?
YES -
Go to Step 8.
NO -
End.

8. Replace A/F sensor. Air Fuel Ratio (A/F) Sensor Removal and Installation
Check DTC.

Is DTC P0420 still detected?
YES -
Substitute a known-good ECM and recheck.
NO -
End.