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2002 Honda Civic P0420 Catalyst System Efficiency Below Threshold

I own a 2002 Honda Civic LX. My Honda recently failed the smog check due to the Check Engine light and trouble code P0420. I have 200K on engine. It burns a little oil (2k to a qt), but runs great. I just replace the cam angle sensor (top dead sensor). It was running like a clogged CAT, only when it was very hot outside. I replaced the sensor and it runs great now. I wonder if running it under heavy load with the bad CAS did damage to the catalytic converter.
Answer:

Both the oil burning and the defective camshaft position sensor would have hurt the CAT. A defective camshaft position sensor can cause problems ranging from no spark combustion conditions including excessively long cranking time when starting cold, rough running, poor idle, stumbling or hesitation, mileage drop and stalling upon acceleration. However before replacing the catalytic converter we recommend also looking into perhaps a defective rear oxygen sensor. Having leaked oil into the combustion chambers and through the exhaust system may have contaminated your Honda's oxygen sensor. With a defective (out-of-range, weak, lazy) rear oxygen sensor your Civic's ECU may think the CAT is damaged when in fact the sensor is not functioning properly. posted by SmogTips Support

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