Oxygen Sensor?

[Nate R]

My Hyundai Accent has 160K miles. I've had it since 86K on the odo.

A couple months ago, the Check Engine light came on. Pulled the code and IIRC it was an 02 sensor code. I reset it and the light didn't come back on for a month, so I figured it was a stray data # that came through the ECU or something. Light popped on after that month or so. (I drive 2400 miles+/month) So I again cleared it. That was a week ago.

I have a Scangauge now, and after several hundred miles, it still shows the ECU as "Not Ready." How long should this take!?

Either way, I'm assuming from what I know now from what I've read here that the O2 sensor is likely on it's way out? (I've never replaced either of them on this car)

Reason I really suspect this is I've been driving MUCH better for FE, yet see no improvement. I get ~36 MPG over time whether I do 72 or 60. That does NOT seem right at all. In the past when I would even slow down to 67 instead of 70-72 and take it easy, I could get 39-40 MPG easy.

Does it make sense that a near-bad 02 sensor could cause this, but not throw on the Check Engine Light right away?