P0420 code

[Rusty]

2001 STS , 95,000 miles. I replaced a destroyed catalytic converter ( Eastern Catalytic converter p/n 50410 ) and removed the resonator which was clogged with debris from the cat. After about 10 days PO420 code appears, scan tool indicated problem with left bank - and the front O2 sensor was replaced. Code set again, same O2 sensor replaced (?) at no charge. My mechanic says scan tool shows the sensor(s) working O.K. Code returns again - now what ?

Any comments or help from the brain trust is appreciated.

[JimD]

2001 STS , 95,000 miles. I replaced a destroyed catalytic converter ( Eastern Catalytic converter p/n 50410 ) and removed the resonator which was clogged with debris from the cat. After about 10 days PO420 code appears, scan tool indicated problem with left bank - and the front O2 sensor was replaced.

What specific code pointed at the front O2 sensor?

Your P0420 is pointing at the catalytic converter;

P0420 - Catalyst System Low Efficiency

The test for setting P0420 involves all three O2 sensors.

How are the codes being read? Codes can be displayed on your DIC. Here's how;

http://www.cadillacforums.com/forums/cadillac-tech-tips/172511-how-pull-codes-98-04-sevilles.html

[Rusty]

The mechanic used a scan tool and stated that bank 1 sensor was suspect. I was told that the 2 front sensors were replaced-

but that is not definite. He explained to me that all the sensors were functioning.

[fonz15x]

The mechanic used a scan tool and stated that bank 1 sensor was suspect. I was told that the 2 front sensors were replaced-

but that is not definite. He explained to me that all the sensors were functioning.

How did this turn out for you? I just replaced my cat about 2 months ago with a eastern cat and the down stream o2 sensor and just got the p0420 code. about a year ago I replaced the cat the first time, this is now my second time. Amy suggestions on what it could be. I hooked my car up to a scan tool that gave the voltage reading of my o2 sensors, the upstreamd ones were jumping around like i would have thought they should, nothing looked lazy. But the downstream one jumped around just as much, is that bad o2 or cat. I dont really get it. anything that someone is will to help me with would be great