I am looking for a little advice here. 04 RX8 threw a P0420 (Cat) code over the weekend. I was reading that it could possibly be the O2 sensors or the cat itself. What is the best way to test what is truly wrong? I don't want to replace one thing have have it be the other.

 

unbolt the cat, look inside. If there's pieces bouncing around, it's the cat.

 

put tape over the light

 

Mode 6 data.

 

Put tape over?

Mode 6?

At least one of the comments was real advice.

 

Since you don't want to search....

http://www.finishlineperformance.com...4-08-1924g.pdf

Read the first & second page thoroughly to see how Mazda techs check the cat converter using Mode 6 data.

And here's a wiki link to Mode 6 data:
http://en.wikipedia.org/wiki/On-boar...e_of_Operation

 

if you r going to look inside the cat pull the o2 sensor and look thru the hole.
when mine failed it looked normal thru the end but was completely melted
inside.