I have an off road H-pipe, MAC, and a 3 inch MAC cat back system on my car. The rest of the exhaust is stock. I'm getting a code of P0420 for an exhaust sensor. Two of the O2 sensors have already been changed and the code is still coming up. The one on the driver's side pipe and one upstream. I'm wondering if I need a new MIL eliminator for the combo???? Anyone know if if that would fix the problem for this particular code? There are no catalytic converters on the car.