a friend of mine has a 01 gt and we put an off road h pipe on it about a year and a half ago. my question what could cause the engine light to come on a year and a half later,we did buy the mil elim and at first i thought that maybe one went bad so we swaped with another one. the light came back on,so were kind of stumped. the code is heated circuit sensor malf. bank 1 downstream. any help would be much app. it comes on after you get on it and start to decel