My car was recently rebuilt and is running very well. However, it's throwing two codes:

1. P0133 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
2. P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

These are slow codes that clear, but come back on after a few miles of driving.

As the engine was being reassembled (due to hydrolock two months ago), there was a bit of water pooled in the cat. Is it possible that the water trashed the cat? Or my oxygen sensors? Or all of the above? Presumably, it's been sitting there for the past two months, so that seems likely.

Any advice would be much appreciated. Thanks.

 

I'd try replacing the sensors first.