Battery Replacement cause code 420 to trigger?

Question

I have a 2004 Prius that has 134,000 miles.  We recently were told we needed to replace the battery- we did this and within a day of taking it home the check engine light came on.  We took it back and 5 codes showed, they told me that they cleaned the fuel injector and it was very gunky so it was "just shooting poop" out and the light should not come back on.  The light has been coming on and off for weeks and now tends to stay on within 10 miles of the reset.  There is only one code now P420 the Catalytic Converter.  Could something the shop did replacing the battery possibly cause this?

Answer 1

P0420 Catalytic below threshold.

Just replacing the battery would not cause a P0420. Having a misfire event or rough idle or anything that will take the engine fuel trim out of control specification such as shooting poop will degrade the catalytic convertor.