fixing ecu code problems

i finally was able to locate my car’s ecu thanx to the help of fellow members. now i need to know exactly what’s goin on with my car. The first code i got was 12 and that means it’s the exhaust gas recirculation (egr) system. The next code was 43 which is the fuel supply system. I would like to know what things these two systems include and what might be goin wrong with them. any help will be greatly appreciated.