This car had been getting 23-26 mpg. It dropped to 20 not long ago. Since I had the tool I scanned the o2 sensor performance both before and after the milage change. I think that one bank has either a bad o2 sensor giving too much gas or I have a bad o2 sensor, but which one? I have drive test response curves for all four sensors but do not have a resource to understand the meaning. Any help out there?
Since the computer would indicate a problem and it hasn’t, you may have to look elsewhere for the problem. The o2 sensors aren’t the only thing on the car that can affect performance. The front end alignment, worn ball joints and especially tie rod ends can lose the gas mileage in a hurry. The key thing is the readings you took. I know it takes time and effort, but you don’t say what the readings were. Is your OD working? Some cars just hit a wall for performance or economy and the good turns to bad and just stays there. I hope there is help out here.
I’d start by doing a basic tune-up if it hasn’t been done, including the air filter if it needs it. If the motor’s out of tune, it will be reflected in the 02 sensor reading. If the check engine light isn’t on and there aren’t any serious drivablity issues, using the engine scanner is probably overthinking the issue.
If you don not have a check engine light your engine is operating within its normal operating parameters. Stupid q but have you changed your tires during this changeover or ever checked tire pressure.
your post is pretty fuzzy to me.
have you actually scanned the car for codes and if so, what are they?
why are you guessing at an o2 sensor problem when a scan should point out which one is at fault; if an o2 is even faulty in the first place.
o2s seem to be the whipping boy when a performance problem exists.
i’ll second andrew’s suggestion about checking tire pressure and don’t consider it a stupid question at all.