Hi,
I have a 2005 Mustang GT 4.6 that is stock, and I was getting a few codes related to O2 sensors. So I put new O2 sensors, upstream and downstream. Most of the DTC's went away, but I still get PO135 and PO155. These are sensor heater related codes, and do not affect performance of the engine. I have troubleshot as best that I can based on what I know, and I have traced the wires into the harness and nothing seems problematic. Just crunchy tape. The engine has 190k on the odo, I have...

Troubleshooting O2 sensors