Checking the O2 Sensor

[rxm6]

I've started to get about 18-20 mpg so the first thing I thought was the o2 sensor, being that the car is 9 years old. Is there anyway to check the o2 sensor before I actually spring the 100 bucks for one? Can I check resistance or voltage?

[Beancooker]

If the o2 sensor is bad, usually you'll throw a code. I'll see what I can find about checking resistance or voltage.

[maxhopper]

If the o2 sensor is bad, usually you'll throw a code.

Even if the O2 sensor is getting "weak" and is slow in relaying the correct voltage to the ECU, it will set the CEL.

[rxm6]

So what's up do you think? Why the poor mpg?

[maxhopper]

Is the 18-20mpg city or highway? Do you have a manual or automatic? How many miles does your car have? When was the last time you replaced the spark plugs? When was the last time you replaced the air filter?

As you can see, we need a little more info.