1998 Honda Civic po 421 code

1998 HONDA CIVIC
180,000 MILES • 4 CYL • 2WD • MANUAL
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HFP65M
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my civic has check enginle light & no 1 knows y, i replaced all wires, sparks, distributor, cap & misfires are gone but engine light still reads 421, is this the front o2 sensor or the rear (downstream sensor) or do i really need a new cat? thanks
Jul 1, 2009 at 1:17 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.
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BLUELIGHTNIN6
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You will need to test the sensors to make sure it isn't a bad cat. converter throwing the O2 code instead.
Jul 1, 2009 at 1:29 PM
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HFP65M
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how do u test an O2 sensor, thanks, im new @ this
Jul 1, 2009 at 2:31 PM
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BLUELIGHTNIN6
  • AUTOMOTIVE REPAIR CONTRIBUTOR
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No problem, we have a page for that! Check out this link below, it will teach you how to test O2 sensors.

https://www.2carpros.com/how_to/how_to_test_oxygen_sensor.htm
Jul 1, 2009 at 8:27 PM