If an O2 sensor is it will it always turn on a check engine light on 2003 Ford Taurus

The thing is when I start reving at about 5000 my car trys to shut off but I think it is an O2 and how many are there anyways?
And it also starts doing the same thing as I am slowing down almost as if it doent know how much gas to send to the engine.
The mechanic said one O2 sensor wasn't working properly but I dint want anymore testing because it was costly

Asked by for the 2003 Ford Taurus
agree get diag codes to proceed. there are test procedures for each circuit on o2 sensors
2 more answers
Why are you hitting 5000 rpm?
Testing is a lot less costly than guessing! That is all we can do without some test info. Did you get any trouble code numbers for the check engine light from the mechanic?
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