My wife's RDX has thrown the CEL several weeks ago. I had it hooked up to a scanner and it had two errors listed for P0420, Bank 1 and 2.

I've done a good bit of searching here and concensus seems to be it's either the cats, o2 sensors, or maybe some bad gas? We only run 91 octane from the same gas station.

RDX has 85k on it, original plugs/wires/etc...probably due for a tune up. It's thrown this code before but it went away on its own. Lately her MPG's have dropped a noticeable amount...used to average around 20 or 21 bit lately it's been more like 16 or 17. Gas mileage usually drops a little here in the winter time when they switch to a winter blend of gas but this seems a little excessive so maybe there's something to the bad cat with the gas mileage decrease.

Thoughts? Does P0420 usually throw for banks 1 and 2 at the same time?

 

Anyone?

 

I'm not too sure if it is normal to throw both codes at the same time. Nonetheless, you could be looking at a new oxygen sensor, or at worst, a new catalytic converter.

I believe you can find the pricing for one here. It is item listed as #1, for a price of 253.56

 

In this case I'm assuming banks 1 and 2 are referring to the pre- and post-cat O2 sensors. If so, failure of the pre-cat sensor is very rare and it's even more rare that both would fail at the same time. That said, the pre-cat sensor monitors your a/f ratio and adjusts fuel accordingly...if that's off it could definitely explain your fuel economy issues. BUT - you may need to do some additional research to see if it's indeed the sensor itself or something else.