I recently replaced the drivers side CAT and both upstream O2 sensors . The cat was cracked and rattling. The drivers side sensor 1 had a bad heater circuit (Po135), and the O2 sensor 1 on the passengers side would only read .07v constant. where the other three were reading .1 - .7volts.
I replaced both upstream O2 sensors with NGK sensors, and ran another scan today . bank 1 was fine .1 - .7 v (both) , but bank 2 sensor (one) upside was staying at .070 v and sensor 2 downside was .1 - .7 so I assume I have more problems. since the brand new sensor in bank2 sensor one is still reading .07 constant.
What do you think?