P0420

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).
2. Do a DTC CLEAR in the CLEAR MENU of the Honda PGM tester or the HDS.
3. Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
4. Test-drive under the following conditions.
- Engine coolant temperature more than 158 °F (70 °C)
- Transmission in 5th gear (A/T in D position)
- Vehicle speed between 50 mph (80 km/h) and 55 mph (88 km/h) with cruise control
- Drive about 2 minutes, then decelerate for at least 4 seconds with the throttle completely closed, then accelerate to 55 mph (88 km/h) for 20 minutes with cruise control

5. Monitor the OBD STATUS for DTC P0420 in the DTC MENU of the Honda PGM tester or the HDS.

Is it EXECUTING?

YES - Go to step 6.

NO - Go to step 4 and recheck.

6. Continue test driving until a result comes on.
7. Monitor the OBD STATUS for DTC P0420 in the DTC MENU of the Honda PGM tester or the HDS.

Is it FAILED?

YES - Go to step 8.

NO - If it is PASSED, intermittent failure, system is OK at this time. If it is EXECUTING, keep driving until a result comes on. If it is Out of CONDITION, go to step 4 and recheck.

8. Turn the ignition switch OFF.
9 Update the ECM/PCM software using the Honda Interface Module (HIM). Refer to Service Bulletin 03-063 for specific model application and procedural information.

Don't replace the catalytic converter unless the software has already been updated and DTC P0420 sets again; doing so wouldn't provide a lasting repair and could result in a warranty debit.

10. Turn the ignition switch ON (II).
11. Do an ECM/PCM RESET in the CLEAR MENU of the Honda PGM tester or the HDS.
12. Do the ECM/PCM idle learn procedure. Programming and Relearning
13. Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
14. Test-drive for about 10 minutes, continually changing the vehicle speed.
15. Check the CATA MON TEMP in the DATA LIST of the Honda PGM tester or the HDS.

Is the temperature OK?

YES - Go to step 16

NO - Go to step 13 and recheck.

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

17. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the Honda PGM tester or the HDS.

Is it EXECUTING?

YES - Go to step 18.

NO - Go to step 16and recheck.

18. Continue test driving until a result comes on.
19. Check for Temporary DTCs or DTCs in the DTCs MENU with the Honda PGM tester or the HDS.

Are any Temporally DTCs or DTCs indicated?

YES - Go to indicated DTCs troubleshooting.

NO - Go to step 20.

20. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the Honda PGM tester or the HDS.

Is it PASSED?

YES - Troubleshooting is complete.

NO - If it is FAILED, check the fuel quality. If it is EXECUTING, keep driving condition continually until a result comes on. If it is Out of CONDITION, go to step 13 and recheck.