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Old 23 Sep 2008, 08:31 pm
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Default 2002 Honda Civic EX check engine light. (P0420)?

I've a 02 honda civic ex & the check engine light is on. It came on after I put a full exhaust system with headers on. I changed all the O2/ oxygen sensors on it and it still is on. The DTC code that I got was P0420 Catalyst System Efficiency Below Threshold. The exhaust system is a racing type. I dont think its reading the excess airflow into the engine correctly. Any suggestions? Thanks in advance.
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Old 23 Sep 2008, 08:46 pm
pry pry is offline
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nao entendi nada
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Old 23 Sep 2008, 09:01 pm
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See if you can borrow or buy an OBD II scanner that features realtime readings. Then observe the values you get for your secondary O2 sensor compared to your primary O2 sensor.Here are samples of voltage readings that seem to be within valid threshold on my civic (non modified)rimary O2 sensor (volts)0.095, 0.855, .075, 0.835secondary O2 sensor (volts)0.055, 0.095, 0.055, 0.115If your readings are extreme, either your new O2 sensors are bad or it's telling the truth.Good luck!
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