Mazda Repair: p0401 every few days, catalytic converters, luck chris

Question
i have a 03 protege 5 that is getting a p0401 puts the eng light on every fewdays have erased it twice-this has been since eng replaced with used unit  

Answer
Hi Ken thanks for asking.
If I recall this code is either a catalyst effieciency code or an O2 sensor. These where bad for blowing out catalytic converters, but Mazda has came out with an updated cat and they should still cover it regardless of how many miles are on the Vehicle. Take it to them and see what they say.
Good Luck
Chris P