Hi,

My protege has P0400 and P0421 for a while. At first, when I reset the computer. It will come back after 50 miles around. Then a mechanic person help me change the cat converter and clean the EGR. But the &0421 also come back every 300-400 miles. It get better,but not fine, no drivable problem. Do you guys have some suggestions about it? (If is it possible for Pre-Cat, The mechanic person saide the pre-cat has a crack,he fix little,but not sure when it will insist).Thanks.