There seems to be a red flag here. Even most cheap obd2 readers
will give a code that will define which sensor it is. If he knew
it was a O2
sensor, he should have been able to look up the code.
Or at least tell you what the code was.
If it was the cat efficiency trigger, he might have wanted to look at
sensor readings on a live scanner to figure out if you
had a bad cat, O2
sensors, or both.
If you have a higher mileage Taurus, replacing both upstream sensors
is not a terrible idea. Might actually improve operations a little if the
old sensors were trashed. But it won't fixed toasted cats. Have you ever
had bad head gaskets or any coolant leaks that could have got into the
Do you really have to fix bad cats? If your in a state that does not
have emission testing, no. Will they make the car run better?
No, as long as there not plugged up. But it will pollute more.
And you will have the nasty light glaring at you every time you start
If your a big picture guy, it would help to get the car scanned with
a live OBD2 scanner and see what the O2
waveforms are, and what
the fuel trims are. That will tell ALOT about the condition of things