Is replacing O2 sensors on Toyota's a common problem? This is my 3rd Toyota that when "check engine" light came on, I was told O2 sensor needed replacing. I believe the mechanic said it was Front, possibly what is called the Bank 1, this time. This gets confusing when I call the parts house and they can't tell me exactly how many sensors my car has. I have been told 2, 3, and 4. PLEASE help me since these parts are quite expensive. What codes should appear when these sensors are bad? How many sensors are there? Should you replace all of them at the same time? What happens if you don't replace them? Is there a way to check the sensors periodically to insure they are performing correctly?
The only difference in the function of the car is a decrease in my mpg, that I have noticed. Other than that, car still runs great.
Thank you in advance for your assistance.