p0139 and p0138 codes

What happens if you don't replace them mainly is you lose out on driveability in fuel economy and engine power. Also you may tend to add to environmental toxins since the O2 sensors are the hallway monitors for exhaust gases, they tell the computer how much oxygen is contained in the exhaust and the computer adjusts fuel flow accordingly with additional input from so many more sensors -- about 7 to 20 or more depending on what vehicle we're speaking of. So mainly fuel economy and power will suffer. ln some areas, you will not be able get the car to pass inspection, thats only if your area has state inspection for emissions.