2000 Mazda Protege code p0420

The means that the Catalytic Converter for bank one is not doing it's job correctly. On rare occasions a leak in the exhaust can cause that code but 95% of the time that is a bad Converter.

there is black sooth in the exhaust do you think its clogged?i want to figure out why the cat is bad before i put a new one .

what can causes a cat to go bad thank you

There is black sooth in the exhaust do you think its clogged?I want to figure out why the cat is bad before I put a new one. i checked the temperature of the converter at the outlet it was 540 F

What can causes a cat to go bad

thank you

Any sort of contamination from a malfunctioning engine will take out a Cat. If you have any misfiring or coolant being burned, that will contaminate it. Just seeing black soot doesn't mean much. All exhaust has soot in it.

ok so i need a scan tool to do that . what is the most best Pc scan tools that i can get?

I put a bottle of techron fuel system cleaner and the check engine light did not come back . all monitors are ready . what you think ?

There is no such thing as "Mechanic in a Can". It will be back.

what is the first thing that i need to check first before i replace the catalytic

For any leaks in the exhaust near the converter.

the check engine light went off now . is this normal and what could causes it?