Got a MIL/CEL w/ a P0420 trouble code on my '04 WRX...Suggestions.

[Dr69er]

Hi Fellas,


I had replaced a upstream Oxygen Sensor on it several months ago (on my '04 WRX) and everything went well.

Fast forward to about a week or two weeks ago got a MIL/CEL, and said to myself WTF now...got my scanning
tool out and it read P0420 trouble code (Cat. Converter, [possibly downstream O2 senor] below threshold B1/B2).

So I'm thinking...I had recently crossed a flooded exit ramp on a highway which submerged the whole exaust system
for about 3-5 seconds and I am wondering if water got in the Cat Converter/O2 Sensor and if that had caused the
problem...or maybe not...suggestions ?

Thanks for any help/suggestions.

[Obeisance]

Do you suppose that there is any chance that the water somehow damaged the electrical connections for the sensors? Maybe rust on old wires, or a short circuit? Did your recently installed O2 sensor have wires come loose over a few weeks?

[Dr69er]

Do you suppose that there is any chance that the water somehow damaged the electrical connections for the sensors? Maybe rust on old wires, or a short circuit? Did your recently installed O2 sensor have wires come loose over a few weeks?

Yeah that is a possiblity...It never had a Issue before that (other than the upstream O2 sensor that was replaced after 70K miles), and
after the MIL/CEL lamp was reset it was good for a week or so...It happened only after the ponding/flooding Incident...Hhhmmm.

[Dr69er]

Anyone with other suggestions or experiances...