99 Accord V6 Ex Check engine light code P0420 can mean what?

1999 HONDA ACCORD
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LSH99
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Over the course of the past month my car has been been surging on the freeway ,when giving it gas it idled high. If driven for a longer period of time.Periodically it has jerked and idled low as if it were going to die.Recently I have seen black smoke coming from the back of the engine compartment which smells burnt.I see the black smoke after shutting off the car after driving and it's not a lot of smoke,but nevertheless it is smoking.The oil isn't contaminated and no overheating as of yet.Today Cel came on showing a code P0420. Any thoughts?
Mar 11, 2015 at 11:23 AM
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JACOBANDNICKOLAS
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That code indicates the catalyst system is working below threshold (bank 1). The following things can cause this code.


- Intake leaks
- Faulty fuel injectors
- Fuel injector leaks
- Spark plugs may be worn
- Improper ignition timing
- Engine Control Module (ECM) malfunction
Mar 11, 2015 at 11:53 AM
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LSH99
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Do you think a bad O2 sensor may be at fault? If it were spark plugs would that cause any smoke?Thanks!
Mar 11, 2015 at 1:07 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,244 POSTS
An O2 sensor could have something to do with it, but that isn't the code you are getting. As far as the smoke, it sounds like you may have a small oil leak from one of the valve covers. Check for that first.
Mar 11, 2015 at 10:26 PM
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