DTC Troubleshooting

Control System DTCs

DTC Troubleshooting: P0420

DTC P0420 : Catalyst System Efficiency Below Threshold

NOTE:
* Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information How To Troubleshoot The Fuel And Emissions Systems.
* If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot them first, then recheck for DTC P0420.

P0137, P0138: Secondary HO2S (Sensor 2)

P0141: Secondary HO2S (Sensor 2) heater

P0300: Random misfire

P0301, P0302, P0303, P0304: No. 1, No. 2, No. 3, No. 4 cylinder misfire detected
* Poor quality fuel may cause this DTC.

1. PGM-FI system check 1:

PGM-FI system check 1
-1. Turn the ignition switch to ON (II).

-2. Clear the DTC with the HDS.

-3. Start the engine. Hold the engine speed at 3,000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.

-4. Test-drive under these conditions:
* Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
* A/T in D, M/T in 5th
* Vehicle speed between 45-75 mph (70-120 km/h) for 5 minutes or more with cruise control set
* Vehicle speed between 55-75 mph (90-120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times
* Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set

-5. Monitor the OBD STATUS for DTC P0420 with the HDS.

Does the HDS indicate FAILED?
-YES- Replace the catalytic converter Service and Repair, then do the repair verification.
-NO- If the HDS indicates OUT OF CONDITION, go to step 2 on this step and recheck. If the HDS indicates PASSED, intermittent failure the system is OK at this time. If the HDS indicates EXECUTING, replace the catalytic converter Service and Repair, then go to step 2.

2. PGM-FI system check 2:

PGM-FI system check 2
-1. Continue test-drive until a result comes on.

-2. Monitor the OBD STATUS for DTC P0420 with the HDS.

Does the HDS indicate FAILED?
-YES- Replace the catalytic converter Service and Repair, then do the repair verification.
-NO- If the HDS indicates PASSED, intermittent failure, the system is OK at this time. If the HDS indicates EXECUTING, keep driving until a result comes on. If the HDS indicates OUT OF CONDITION, go to step 1-4 and recheck.

Repair verification (OBD STATUS check):

-1. Turn the ignition switch to ON (II).

-2. Reset the ECM/PCM with the HDS How To Troubleshoot The Fuel And Emissions Systems.

-3. Do the ECM/PCM idle learn procedure ECM/PCM Idle Learn Procedure.

-4. Drive the vehicle until the result of CAT MONITOR CONDITION in the DATA LIST on HDS indicates OK.
NOTE: Test-drive may to 10 minutes or more.

-5. Test-drive under these conditions:
* Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
* A/T in D, M/T in 5th
* Vehicle speed between 45-75 mph (70-120 km/h) for 5 minutes or more with cruise control set
* Vehicle speed between 55-75 mph (90-120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times
* Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set

-6. Monitor the OBD STATUS for DTC P0420 with the HDS.

Does the HDS indicate PASSED, FAILED, EXECUTING, or OUT OF CONDITION?
-PASSED- Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated, go to the indicated DTC's troubleshooting.
-FAILED- Go to step 1 and recheck.
-EXECUTING- Keep the test condition until a result comes on.
-OUT OF CONDITION- Meet the test condition, and check the OBD STATUS again.