[jpit]

I agree with William_Wiles. Have it diagnosed correctly. Most likely the cat is the problem. I'm also a firm believer that the EGR valves/ clogging problem leads to premature cat replacement.

The Honda TSB 03-073 that the Honda service guys use tells them to replace the cat for a DTC P0420 so that's what they will do. Cats are covered under 8/80K miles warranty.

 

[jpit]

jkp, I don't think that there are a lot of bugs in the OBD2 system on the ODY. I do think that the OBD2 'senses' a few problems that are genuine at the time of failure. As William_wiles indicated in the last post, after several OBD2 drive cycles if the problem that originally set the Diagnostic Trouble Code is no longer there then the 'check engine light' is turned off. That would be the correc way for it to be handled.

For your P0420 code there are a number of reasons why it can be set. The downstream O2 sensor is the item that determines whether your catalytic converter is efficient. It's rarely the 'cause' of the P0420. It's only job is to 'sense' a deteriorating catalytic converter. I won't go into how it does it as you may have read about it anyway. Occasionally this sensor does fail but not as often as the upstream O2 sensor whose job it is to feedback the Air/Fuel ratio to the PCM.

I have an O2 eliminator on my downstream O2 sensor so I don't get the P0420 anymore but that's a whole different story.