I just purchased a 2003 GT which the previous owner installed aftermarket catless exhaust. He has the after cat o2 sensors installed with mil eliminator, however my check engine light still comes on throwing codes for both the after cat O2 sensors. I've read in many articles that most vehicles 2001+ have a more advanced program for running the after cat o2 sensors and the mil eliminator wont trick the PCMinto beleiving there fine. if thats the case i understand a tune would be necessary to recitfy this. if not my question is; Does the O2 sensor have to function properly in order for a mil elimintor to work?