Code P0420. Catalyst System Efficiency Below Threshold (Bank 1)

Hi anoble1,

Thank you for the donation.

P0420 is a fault with the catalytic converter and not the O2 sensor. Check for leaks at the catalytic converter.

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

1. Reset the ECM/PCM.

2. Start the engine. Hold the engine at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.

3. Except F23A4 SULEV engine: Test-drive at 40-55 mph (64-88 km/h) for approx. 2 minutes. Then decelerate for at least 3 seconds with the throttle completely closed. Then reduce the vehicle speed to 35 mph (56 km/h), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result.

F23A4 SULEV engine: Test-drive at 50-55 mph (80-88 km/h) for approx. 2 minutes. Then decelerate for at least 4 seconds with the throttle completely closed. Then accelerate to 55 mph (88 km/h), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result.

Is the test result FAIL?

YES -Check the three way catalytic converter (TWC). If necessary, replace the TWC.

NO -Intermittent failure, system is OK at this time.

Not all scanners are able to determine the catalytic condition. I am not familiar with the mentioned so do not know if it has that capabilities.

If the code comes back on, it means fail.

Some after market catalytic converter are not compatible as it might be working out of the specified range.

You mentioned replacing with a new catalytic converter, does it come with a warranty?

If yes, you should get them to replace it and retest. The ones installed could be faulty.

Not really necessary but after market comes in different quality and the installation work plays a part