Hello all,
I have tried to dig through the varius posts to find my posts. Either my concern is different, or I do not have the technical ability to understand how they relate to my plight. A novice I am, so I added all the details I could think of that may be important.

My 2004 WRX Wagon with 185,000 miles has a case of the CEL code P0420 and has not responded to treatment. Time for a different approach?

Since the check engine light has come on about 3,000 miles ago in late fall, the 02 sensors have been replaced, and after 2 after-market catalytic convertors were tried, a dealer version was put on last week. Yes, that's three different cats installed. Each time, the CEL is back on soon after 100 miles. I did not check the codes on the prior CELs, but the most recent is P0420.

The same local mechanics shop that has always serviced this WRX now suspects an electical issue, but I have yet to take it back. I am wondering if enough attention is being paid to potential underside damage in the 2 months prior. First incident was dead center and loud strike of a truck tire tread one night on the highway. Second incident was a doe laying down in my lane - thankfully no antlers on that one! On both, I noticed some bump noises, but no lingering smell, damages, or handling issues afterwards. These events were within a few thousand miles of the first CEL that was sporadic at first and then went constant CEL. Not that I think it is important, but I have replaced 3 driver side low beam bulbs, 2 dashboard lights, and have intermittent cruise control engaging all in the last 2 months.

Any advice on getting the CEL fixed so I can pass inspection and surpass 200,000 miles?
-Ask for a closer inspection for exhaust line damage?
-Could it simply be an electrical malfunction somewhere?
-Different O2 sensors worth a shot?

Thanks for your advice,