Pontiac Repair: Error codes and fender shields, mass air flow, inner fender

Question
I have a 2007 G6 4 cylinder, the computer diagnostics are sending error codes of P0101, P0012, and P300 do any of these codes suggest that the catalytic converter is bad. How does a dealer determine if catalytic converter is bad, is it with computer codes or by just disconnecting things until they find the one it is? I also need to know is there a shield that goes under the radiator to keep water from coming up into engine? Could you give the parts number for the inner fender shield passenger side and the shield that goes under radiator if there is one? Or at least tell me what they are called? I have seen them called shields and inner wheelhouse wells. Thank you.

Answer
Hey Jay:

The p0300 is a misfire code random cylinders. P0101 is a Mass air flow code and the p0012 is not a code for a 4 cylinder engine. did you use a generic code reader? if so that could be a false code set. There is a closeout panel/air dam that goes under the radiator but it doesn't keep all the water out of the engine compartment. The parts for the fender your looking for are called fender liners. I can't help you with part #'s I just fix 'em I don't look up the parts.