Rep Power: 0

Obviously no one can diagnose my Civic without seeing the car. Before I take it to the mechanic I wanted to see what the forum's thoughts were. I have a P0420 and P0430 code from the local auto parts store. My guess is its my backdraft O2 sensor, and not my catalytic converter. Also, I think my valve cover gasket is starting to fail, so perhaps its getting oil into the exhaust.

Lastly, I've reset the code several times and between resets it took 3 months before it came back on. Only recently does it come back on immediately after resetting it and then driving it.

Just looking for thoughts and opinions. Thanks.

 
Rep Power: 174

You could at least take a look at the sensor. If oil is getting into the exhaust though, then I think that would explain why the sensor isn't happy.

 
Rep Power: 518

Start over, check with another scanner.
You can't have a P0430. Someones code reader is lying.

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Most cat codes are really set by a bad cat.
The biggest exception to this is exhaust or air leakage anywhere between the cylinder head and the cat, and up to at least 2 feet behind the rear sensor.

A cat can be ruined by other causes though. Misfire, oil consumption, contamination/poisoning, etc.
But even if the root cause is something else (such as misfire), a bad cat is still a bad cat.
Check out this bulletin: http://www.tegger.com/hondafaq/p0420/A05-027.pdf
(Notice in the bulletin: even though the root cause is in loose igniter connections, if it threw a cat code it gets a cat. Simple.)

Most of the time, replacing sensors is a waste of money. Even bigger waste if you get the wrong sensors.
There are a whole bunch of codes that deal with JUST the O2 sensors themselves. Got any of those codes?

Most valve cover leaks don't end up on the O2 sensors unless it's a huge leak....Get under it and look, see if they are saturated in oil residue and grime.