oxygen

I have 2004 accord LX 4 cylinder. Few days back got engine light. Code are in sequence P0171 and P0420. Is problem with MAF sensor, Cat or O2 sensor? I try to diagnosis through my OBD reader. I'm getting some reading for MAF sensor and O2 1x2 sensor. But no reading for O2 1x1.

New to the forum and recently bought an '03 Accord with California Emissions. I live in the EasT Coast. P0420 code pops up so I replaced the o2 sensor with a Denso 234-4363 Oxygen Sensor, which is a California legal o2 sensor. CEL came back on and did some thermo tests on cat, found out it was...