I own a 2016 Nissan Altima SR 2.5. The O2 sensors keep failing ( 5 sensors in 18 months). Nissan reprogrammed the ECM and it didn't do anything. Nissan after there tech last inspected the car is blaming the O2 sensor failures on a replacement piece of exhaust with the 2 O2 sensors on it and the cat. This was replaced by Lou's Custom Exhaust after a accident that crushed the factory exhaust. Nissan claims they reduced the internal diameter of the exhaust by welding the new pipe inside the doctors pipe where the two pieces were joined together. Is this possibly the cause of these frequent O2 sensor failures. The exhaust was repaired at 700 miles and O2 sensors were fine until about 25,000 miles. It now has 37,000 miles and another O2 sensor that was replaced 3 months ago is showing failure code. This will be the 6th O2 sensor gone bad. Help !