2006 nissan titan 5.6 se..codes po420 and po 300

Did you try looking up the codes online ? Try www.TitanTalk.com or www.check-engine-light.com for assistance on that vehicle specifically. •P0420 Catalyst System Efficiency Below Threshold (Bank 1), •P0300 Random/Multiple Cylinder Misfire Detected - - Random Misfire problems can be fixed by simply replacing plugs, wires, and coils. Typically those are the first things to check. Other things to check normally include the fuel injectors themselves, then your O2 sensors. There are quite a few things to check - compression, valves, intake manifold gasket, etc. and if you aren't up to the task it might be better off to take it to an experienced, trusted technician for a proper diagnosis, even if you perform the repair yourself.