Bad Pre-Cat....Most likely anyway. Possibly o2 sensor but unlikely since it's "Below Threshold"
That code means the first Catalytic Converter, one right off the manifold isn't heating up enough to convert toxic exhaust emissions into non-toxic substances. The core or "substrate" has a special coating on it that when heated it reduces carbon monoxide(CO), unburned hydrocarbons(HC), and oxides of nitrogen(NO, NO2, & N2O) to produce carbon dioxide(CO2), nitrogen(N2), and water(H2O).
So basically the pre-cat is bad or one of the oxygen sensors is gone. Either way you should be under warranty. I wouldn't take your car to Mitsu with your new intake though. The may give you a hard time because of it.