Usually I like to change the oxygen sensors around 100,000 miles, but due to procrastination and no check engine light, and this is the first day in months when the weather is suitable. I changed the upstream sensor with hopes of better gas mileage. My car is a 2005 LGT wagon with 136k on the odometer. Can I expect any improvement in fuel economy? I have not done the downstream sensor for 2 reasons: If I got a check engine light I'd have to read codes to figure which went bad, and looking at the location of the downstream sensor, this looks like a job best done on ramps or a lift. I read the downstream sensor is really only telling you if there's an emissions problem, and if I had a problem the car would throw a code. The same article said the upstream sensor does all the work with the car's computer and helps preserve the catalytic converter (I tend to believe this simply by looking at the price of each). Should I be in a hurry to do the downstream sensor? The car seems to run smoothly and I haven't gone far enough to see fuel economy results.
By the way, the replacement was done by turning the wheels right and opening the access door. Just be sure to spray the base of the old unit with PB Blaster or a similar product. It did come loose with the special socket and a 12" ratchet wrench.