CEL Code P0420

[kuche]

I have a 2001 Boxster S. It has been running fune until this week, when I got a CEL light. I read the code and it is a single code, P0420 Catylist system eff below threshold Bank 1. Any suggestions on next steps? I assume this indicates a bad CAT - does this need to be replaced or is there some other fix? Can it be driven like this or should it be fixed asap?

thanks

[JFP in PA]

It could be the three way cat (bank 1-3), but the diagnostics manual suggests five seperate test sequences that should be run (some require either a PIWIS or Durametric Pro system to run) involving the EVAP system and O2 sensors before trashing the cat (that is because the TWC is one expensive part number).

[kuche]

Thanks JFP - any harm in driving the car with this issue?

[boosted 89]

P0420 means either the catalytic converter isn't doing its job properly or the post cat o2 sensor isn't reading the gases properly. The post cat o2 sensors are only used for monitoring and not engine tuning like the pre cat o2 sensors so it will not harm the engine or cause driveability issues. Only issues would be emission testing if applicable or worst case the cat could break apart inside and plug up the exhaust which you would notice with possible misfires on one bank or a drastic power reduction under load. Most post cat o2 sensors will set a code if the sensor doesn't change enough and if the sensor changes to much it will set the p0420 code depending on which bank.

[JFP in PA]

Originally Posted by kuche

Thanks JFP - any harm in driving the car with this issue?

Probably not in the near term, but if the cat is toast, it could break up eventually, which would lead to other problems.

[kuche]

Thanks - the code has cleared itself - not sure if thats good or bad but i sleep better thinking that its a good thing!

[JFP in PA]

It could have been a "ghost" code.