What is DTC PO420 on a 2000 Camaro?

P0420 usually points to a failed catalytic converter, if the exhaust system is intact, that is. Exhaust leaks in front of a catalytic converter can affect the O2 readings and at times throw a false code.

P0141 indicates only the heater circuit of the o2 sensor has a problem. Usually it's the element in the sensor, and replacing the sensor would fix that, but it doesn't rule out a harness issue or a short in the wiring