What causes OBD code P0420?

Answer 1

This code means that your catalytic converter efficiency has dropped below the nominal value. p0420 is a generic code for the catalyst to indicate that you need to investigate a potential problem with your emissions system associated with the catalytic converter.

Code P0420 means "Catalyst System Efficiency Below Threshold (Bank 1)"

P0420 is actually Catalyst System Efficiency Below Threshold Catalyst System Efficiency Below Threshold.

This means that the secondary O2 sensor detects that the catalytic converter isn't working as efficiently as it should.

This engine code can be triggered by any one of the following:

1.) The catalyst in the catalytic converter is cracked, clogged, or otherwise damaged.

2.) The secondary O2 sensor is malfunctioning.

3.) There is an exhaust leak.

4.) The computer unit is faulty.

Trouble code P0420 means: Catalyst Efficiency Below Normal (Bank 1)
Code PO420 is catalytic converter efficiency low bank 1, sensor1. You did not state as to the year,make and model of the car as well as the engine size. I am a member of IATN and the majority of there fixes was related to someone installing an AFTER MARKET converter. There is a big difference. I strongly suggest that you go to a repair shop with the proper equipment as well as a very good tech to diagnosis the problem. You could replace parts and never fix the problem.jd1709