1997 Chevy Cavalier catalyst converter

DAVIDFARR3000

MEMBER
1997 CHEVROLET CAVALIER
4 CYL
FWD
AUTOMATIC
195,000 MILES

Hello, I am having a problem with my car which involves the code P0420, catalyst efficency below bank 1, what is the cause of this? I replaced the oxygen sensor that goes into the manifold, is there another one at which I need to replace? Or is the problem with the catalytic converter itself? If that is the issue can I remove it and replace it with a pipe? I live in minnesota and am pretty sure that that is legal, I would appreciate any advice, thanks

3 Replies

MMPRINCE4000

MECHANIC
8,549 POSTS

The code indicates the downstream (after convertor)O2 sensor is getting abnormal readings, out of range.

Most likely the sensor is bad, but could be the convertor. A backpressure test will tell you if the convertor is bad.

It is illegal to remove the convertor, this is a Federal law, not a state law.

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Monday, September 28th, 2009 AT 7:36 AM

DAVIDFARR3000

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28 POSTS

Where can I get a backpressure test done and what would it cost? I live in minnesota

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Monday, September 28th, 2009 AT 11:12 AM

MMPRINCE4000

MECHANIC
8,549 POSTS

Call around and ask repair shops for a quote. Some muffler shops can perform this.

They will probably charge 1 hour shop time, usually $85-100.

If convertor is bolted to exhaust, you can remove it, look inside. Should be a honeycomb, grayish color.
If you see any melting/cracking or sooty material, convertor is most likely bad.

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Tuesday, September 29th, 2009 AT 9:18 AM