To repair a car displaying a P0420 code, diagnose the cause of the code, which is related to the catalytic converter, then replace the part that is malfunctioning, and clear the code. The repair can be completed within one to two days.
- Determine the faulty part
A P0420 code signifies an efficiency problem with the catalytic converter. The most common cause is a catalytic converter that isn't working. Another possible cause is a malfunctioning rear oxygen sensor. Perform a visual inspection of the exhaust system, the catalytic converter and the oxygen sensor. Look for dents, holes, broken wires and any other signs of damage. If there are no signs of damage, use a scan tool to check the oxygen sensor. The waveform from the oxygen sensor should be steady; otherwise the sensor needs to be replaced.
- Replace the part
Buy a replacement for the part that isn't working correctly. If you are unable to replace the part yourself, take the car to a professional technician.
- Clear the error code
Use a scan tool to clear the P0420 code. Start the car, and verify that the Check Engine light isn't on anymore. The Check Engine light may not reappear until the car is driven for a few miles. If the light stays off, the problem is fixed.