Mercury 2001 grand marquis . ...which side is bank 1

Question

I received
a code of p0420 on my mercury...but it doesn't tell me which side or if it's top or bottom or back or front.can you help

Answer 1

P0420 Catalytic below efficiency Bank 1

Bank 1 is where cylinder 1 is located at. ,

 Here is a typical catalytic convertor, you can see the rear 02 sensor, rear 02 sensor are catalytic monitor sensor which monitor the effectiveness of the the catalytic convertor. The front 02 sensor monitor the engine management condition, Whats is marked is Bank 1