Any way to check for faulty Oxygen Sensor?

Hi,

Someone mentioned in a thread I posted that their poor MPG problem was resolved by replacing an O2 sensor.

My mileage is still bad (13.7 MPG now) and I guess I should try the O2 sensors next.

My question is, do you have to just wait until the 'check engine' light comes on in order to get a code that identifies the faulty sensor?

Is it possible to just inspect the sensors visually, or have some diagnostics done by the dealer to find the sensor that needs replacing? I'd like to get the poor MPG problem resolved ASAP and would rather not wait for the 'check engine' light to come on if I don't have to.

Thanks for you time,
CW

I'm not 100% sure, but if it's faulty, something should come up if you get the computer scanned. Go to Autozone or somewhere and they will usually scan your car's computer for free.