I am trying to help a friend of mine on his 1998 Sebring 2.5 liter. It is throwing the code P0420 which is insufficient catalytic convert efficiency. I was going to check the downstream O2 sensor to see if that is it instead of the cat, but when I look at the car, I see 3 o2 sensors. One on each bank and then an additional one just down from the bank 1 sensor before the two pipes merger but WAY before the catalytic converter. My understanding is that it is suppose to be measuring the switching activity before and after the cat to determine if the cat is working. Since it is WAY before the cat, how does it measure the efficiency of the cat since it is just about 1 foot from the first o2 sensor on bank one and before the mergewith thebank 2 cat.

I am used to seeing the o2 sensor before and after the cat. I assume that it works this way since it was built that way but I just don't understand how it can. Can this code be from the center O2 sensor being bad?? Is it the cat???

 

replace the converters.

 

Thank you sir.

Are there 3 or 4 o2 sensors on that car? I was wondering if I just missed finding the top o2 sensor on the back side of the engine.

Are the cats the small short section right after the exhaust manifold or is it the unit located about mid way down the car?? The one mid way down the car seems to far away to get hot enough.

Reb

 

There should be 4 o2 sensors. Two upstream and two downstream.