2002 1500 5.3L 4wd

I am getting a code of P0420. The explanation says something about emissions.

Can anyone steer me in the right direction for repair. O2 sensor maybe?

 

Common DTC on these trucks,
Look at this item first because 75% of the time this is the cause and it is a no-cost repair:

The cause may be due to an ECM ground terminal that has corroded with rust over time. Inspect the main engine wiring harness ground terminal for this condition.

The wire terminal attaches either to the front or to the rear of the right side cylinder head. If the ECM ground terminal has been found to be corroded, then remove the hardware and remove the corrosion then reassemble.

 

Thanks. I will check it out.

Could this also be the reason for pulsating lights throughout the vehicle? Bad Ground connection?