DTC Troubleshooting: P0420 (67)

DTC P0420: Catalyst System Efficiency Below Threshold NOTE:

- If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then recheck for DTC P0420.
  P0137, P0138: Secondary HO2S (Sensor 2)
  P0141: Secondary HO2S (Sensor 2) heater
- Poor quality fuel may cause this DTC.

1. Turn the ignition switch ON (II).

1. Clear the DTC with the HDS.

1. Start the engine. Hold the engine speed at 3,000 rpm (min −1 ) without load (in Park or neutral) until the radiator fan comes on, then let it idle.

1. Test-drive under these conditions:
   - Engine coolant temperature above 70 °C (158 °F)
   - Transmission in 5th gear (A/T in D position)
   - Vehicle speed between 80 km/h (50 mph) and 88 km/h (55 mph) with cruise control
   - Drive about 2 minutes, then decelerate for at least 4 seconds with the throttle completely closed, then accelerate to 88 km/h (55 mph) for 20 minutes with cruise control

1. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the screen indicate EXECUTING?

YES | - | Go to Step 6 .
NO | - | Go to Step 4 and recheck.

1. Continue test driving until a result comes on.

1. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the screen indicate FAILED?

YES | - | Go to Step 8 .
NO | - | If the screen indicates PASSED, intermittent failure, system is OK at this time. If the screen indicates EXECUTING, keep driving condition continually until a result comes on. If the screen indicates OUT OF CONDITION, go to Step 4 and recheck.

1. Turn the ignition switch OFF.

1. Replace the TWC:
   - K20A6 engine
   - K24A3 engine

1. Turn the ignition switch ON (II).

1. Reset the ECM/PCM with the HDS.

1. Do the ECM/PCM idle learn procedure.

1. Start the engine. Hold the engine speed at 3,000 rpm (min −1 ) without load (in Park or neutral) until the radiator fan comes on, then let it idle.

1. Test-drive for about 10 minutes, then it drives, continually changing the vehicle speed.

1. Check the CATA MONITOR CONDITION in the DATA LIST with the HDS.

Is it OK?

YES | - | Go to Step 16 .
NO | - | Go to Step 13 and recheck.

1. Test-drive under these conditions:
   - Engine coolant temperature above 70 °C (158 °F)
   - Transmission in 5th gear (A/T in D position)
   - Vehicle speed between 80 km/h (50 mph) and 88 km/h (55 mph) with cruise control
   - Drive about 2 minutes, then decelerate for at least 4 seconds with the throttle completely closed, then accelerate to 88 km/h (55 mph) for 20 minutes with cruise control

1. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the screen indicate EXECUTING?

YES | - | Go to Step 18 .
NO | - | Go to Step 16 and recheck.

1. Continue test driving until a result comes on.

1. Check for Temporary DTCs or DTCs in the DTCs MENU with the HDS.

Are any Temporary DTCs or DTCs indicated?

YES | - | Go to indicated DTC's troubleshooting.■
NO | - | Go to Step 20 .

1. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the screen indicate PASSED?

YES | - | Troubleshooting is complete.■
NO | - | If the screen indicates FAILED, check the fuel quality. If the screen indicates EXECUTING, keep driving condition continually until a result comes on. If the screen indicates OUT OF CONDITION, go to Step 13 and recheck.