I'm not getting very good mileage in the city in my automatic '04 EXL, about 16 mpg. I've read here that a defective 02 sensor could significantly affect fuel economy, but I would think I would get a message if the 02 sensor was malfunctioning. What's the likelihood of needing a replacement sensor if the car's computer's not picking up a defect? Sparks, air filter and tire pressure have all been checked.

Dismal fuel mileage in pure city driving conditions with 4 cylinder gen 7s seem to be the norm.

Your car doesn't have an oxygen sensor, it's a wideband air/fuel sensor, similar, but different from a conventional O2 sensor.

If you bring it to a shop that has an oscilloscope they can hook it up to the sensor's signal wires, to see if it's signal is correct. Also with a good scanner or HDS (better) they can watch the fuel trim information to see if there's any issues. Usually a slow/lazy exhaust sensor will skew the trims and can affect fuel economy.

Other things to check, brake drag, are any dragging? Engine temperature, does it make it to full operating temperature? What brand and type of tires are on the car? I see a 1.5 mpg drop using my winter tires, alone. And about .5 mpg due to the colder weather. (I have a V6 6 speed) So I've been getting 27.5 to 29 this winter.

Thanks for the advice. I have Michelins on the back and a pair of Falkens on the front (they came with car when I bought it a few months ago), both sets all-season. I may wait till the weather gets warmer before I take it in.

I'd get away from the Falkens. They seem to have a lot of rolling resistance for relatively poor handling.
Michelins, if they're the same as stock ones, are a lower rolling resistance tire, but handle mediocre at best.

If you look for newer tires, and want an "all season" tire, look for one that's considered high performance all-season. Make sure it's got silica in the tire compound. The silica helps with grip in all conditions but it also reduces rolling resistance.

Some good tires in your cars size range are Bridgestone G019 Grid, H rated is more than adequate; Bridgestone RE960AS Pole Position, General Altimax HP ( I was surprised by these, I put them on my mom's EXL4), Yoko Avid H4S.

There are numerous Michelins in that size, but they do get quite pricey and in all honesty, you pay for the name, definitely not for the way the tire performs.

I had same problems with the Falkens on the 03. Current ride has Michelin OEM but when cornering they kind of slip on the road if you force it too much.

Thanks for the advice on tires. The back has Michelin Energy MXV4s...a good tire?

Ok for fuel economy and long wearing for the most part. Relatively poor grip.
They've been changed to Primacy MXV4 I believe now, same tread pattern, same grip, less rolling resistance.