My check engine light came on today so I went to autozone. Code P0420. Catalyst 1/1 efficiency below required level. What exactly does this mean? I have a magnaflow high flow cat that is only six months old. ANY help would be much appreciated.

 

The pre cat 02 sensor is bad or you need an 02 simm.

 

thanks! we'll start with the sensor. You recommend any OEM brands?

 

1/1 is the left upstream sensor. I have had good luck with the Bosch O2s....

 

Like PS says it is the left bank which I forgot to say. However you'll only have one pre cat sensor if its not Cal.

 

Thanks guys. Going to pick one up now.