Oxygen sensors

High consumption, warning light on, you *may* get some running problems, but most of the effects are slow and long term.

Depends on the car and programming, but a dying sensor may give rise to a slow surging when travelling in say 2nd or 3rd fairly slowly (~2000rpm) on a very light throttle. A dead sensor will tend to just give high fuel comsumption.

Both will result in an MOT advanced emissions test failure.

Why do you think you may have an o2 sensor problem?

Tim..

...higher fuel consumption than expected. Thanks, that helped!