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check engine light is on constantly

I have a PO421 code,should I change the lower oxygen sensor?

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3 Answers from these members:
afritz afritz
Providing a complete model number to your question will definitely help an expert better your search. If you would like to reply to this thread with a complete model number included I would be more than happy to assist you. Have a great day.
by afritz afritz Earned 974 community points in Automotive
June 16th, 2011
Answered in 8 minutes
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Manage My Life
2000Ford Focus ZX3.Don't have VIN at this time.
by Manage My Life
June 16th, 2011
Answered in 38 minutes
0 votes
bikerbigpapa bikerbigpapa
No you have an ineffective cat. Contact your dealer for warranty info as the government mandates the manufacturer has extended coverage for emissions issues. They will be able to tell you if it is covered or not.
by bikerbigpapa bikerbigpapa Earned 7,304 community points in Automotive
June 17th, 2011
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