P0420 in 99 Protege lx 1.6

[99protegelx99]

Hey everyone. I have a P0420 code in 99 Protege lx. It has 139K on it and the CEL and code always comes back when I try resetting the codes. I have talked to several mechanics and they assure me that it is the Catalytic Converter and needs to be replaced. However I talked my friend and he said it could be the O2 sensor on the back side of the cat. What is everyones experience with P0420's. Does anyone know if the O2 sensors are fouling or non fouling? Could a rich or lean condition bring out the code? Thanks

[crazycanadian]

98% of the time it's a bad cat. A proper road test and diagnosis with a scan tool and someone that know what to look at will make you 100% confident.

It can be an O2 sensor problem or exhaust leak. But like I said 98% of the time it's a bad cat

[tradosaurus]

Before you replace the CAT watch this video.

[twowheels012]

If you have two converters, most likely the upper one is clogged.

[99protegelx99]

The scotty kilmer option sounds goods. Does anyone know how to take out the converter in a 99 Mazda Protege? What tools would you need to do so?

[99protegelx99]

I don't want to put lacquer thinner in my gas tank I think it could trip other codes...

[tradosaurus]

I did it in my Protege with no ill affects.

[99protegelx99]

Well now I am replacing my Converter. Does anyone know the torque specs for all the bolts around the catalytic converter? or where I might be able to find them...Thanks