Wile back I posted about a emissions problem, Nox high, 2000 & low Hc. Had a new Y-pipe same bends as the high flow but normal cats. Changed both O2 sensors and passed easily. No check engine light before I changed them but the scanner was saying that the rear bank was not correct. Not to bad on the price for the sensors, $79.80 for 2 Bosch units.
Ken