First off, I've only read this with generic OBDII reader. I haven't had Volvo pull the code yet.

I will randomly get the p0420 code, months apart. The first time I got it coincided with an inspection due, so I just cleared it. It re-appeared ~3 months later. Cleared, about a month later it came back. Cleared, about a month and a half later it came back.

As far as I can tell, the cats are fine. The car has 112k miles on it. It seemed to coincide with the really hot weather beginning here in central Texas? Typically it will appear after about an hour on the road continuously.

Anything else this could be symptomatic of? Is it worthwhile to have Volvo pull the code, ie could it reveal more info?

Thanks for any help.

 

Maybe O2 sensor?

 

Thanks for the response tech, you're a huge resource! Do you know if Volvo will be able to see a separate o2 sensor code if it's there (as opposed to the generic p code I mean)?

 

Yes they will. Most Generic scanners will only read half the codes stored in the S40's for some reason.