what does code P0420 mean

Kymberly Miller

Asked by Kymberly Feb 05, 2013 at 01:37 PM about the 2001 Volvo S40 STD

Question type: Maintenance & Repair

my check engine light came on and  i had it scanned and the code was P0420.. what does that code mean?

3 Answers


P0420 - Catalyst System Efficiency Below Threshold Bank 1 -- As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

4 out of 4 people think this is helpful.
Samuel Buck

probley be the front lamda sensor

3 out of 3 people think this is helpful.
Josh Funk

tenspeed is right...sounds like a bad 02 sensor...affects emissions.

2 out of 2 people think this is helpful.

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