upstream downstream? how many? looking at at replacing cat, what sensor(s) do i need? popped a code P0420?

 

Depends on what kind of emissions package you have on yours but seeing as you have an 02, I'd guess you have 3 as a general guess. You can have as many as 4 however it just depends and you'll have to get under and check to see how many you have to be sure. Most likely 3 (2 upstream and 1 downstream.

You don't have to replace the all the sensors I you're replacing the CAT. Just the one the CEL code is telling you.

 

Please list the motor and California emissions if applicable.