OBD code P0420

The ECU has detected that the bank 1 catalytic converter is no longer cleaning exhaust gases as expected.

Estimated severity

Medium

Common symptoms

Steady check engine light
In many cases, the vehicle seems to drive normally
Possible slight increase in fuel consumption
Risk of failing an emissions inspection

Likely causes

Aged, contaminated or physically damaged catalytic converter
Faulty or slow upstream or downstream oxygen sensor
Exhaust leaks before the catalytic converter
Long-term rich running or misfires such as P03xx codes

Recommended checks

1. Check whether mixture or misfire codes explain why the catalytic converter may have been damaged.
2. Inspect the exhaust for leaks before the catalytic converter.
3. Analyze upstream and downstream oxygen sensor signals with a scanner.
4. Check the physical condition of the catalytic converter, including internal noise, blockage and temperature behavior.
5. If everything else checks out, consider replacing the catalytic converter.

What does code P0420 mean?

Code P0420 means the catalytic converter on bank 1 has lost efficiency. By comparing the oxygen sensor readings before and after the converter, the ECU sees that the converter is not storing and converting gases properly. The root cause may be the converter itself, slow or faulty oxygen sensors, or mixture problems that have damaged it.

Try assisted diagnostics