Having problems with your 2002 Honda Civic ?

Replaced catalyst converter, both sensors and still have code P0420 what's the problem

\015 My egines light came on and it indicated a code P0420, Catalyst Effiency Below Threashold Bank 1. I, replaced the converter with a new one and put new sensors on it, both upper and lower. I, replaced the PVC Valve, put new air filter in and I, still have the P0420 code. What else need to be checked?\015 Posted / edited by AnonymousUser on : 10-06-2019

Answers :

Hi there:
The possible causes of this code are: exhaust leak between the exhaust manifold and converter, downstream O2 sensor wiring damaged due to coming in contact with exhaust pipe, or failed converter.

Check for any exhaust leaks and repair as necessary. Check wiring harness at O2 sensor and if damaged repair or replace. Keep in mind that catalytic converter have a 8yr/80,000 mile federal emissions warranty, so if you have less than 80,000 miles this will be covered undered the warranty and would need to be replaced by dealership.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.
Repair Help & Product Troubleshooting for 2002 Honda Civic

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