Someone told me when you get the bad o2 sensor code, if the car runs lousy, replace the front one, but if the car runs well, and the light stays on, replace the back one. Is this true?

Well sort of. If the car has lots of miles (usually over a 100k on a sooby, but they can last to 180K), the MPG has taken a dump, or the light comes one and off over time, it is most likely the front sensor.

 

The rear sensor just monitors the Cat output and will usually outlive the front one. It wont have an effect on performance.

 

Of course you can bench test them.

Someone told me when you get the bad o2 sensor code, if the car runs lousy, replace the front one, but if the car runs well, and the light stays on, replace the back one. Is this true?

no, not every time.

 

first two steps are making sure you don't have any exhaust leaks and reading the code. many chains read the codes free or buy a scanner for $30 off ebay and do it yourself.

If you buy and 02 sensor, suggest you buy one with the correct electrical connector. I have never had any success buying a generic sensor, and soldering the old connector to the new sensor.

And now, the contrarian view (with apologies to Rooster!)

 

Go to Amazon-dot-com and order a Bosch universal, you'll save a ton of money. Be sure to enter your car's information to make sure you get a compatible one.

 

No need to solder (in fact you are not supposed to since the sensor leads are not copper), just use the povided connector and follow their instructions. It's a bit fussy but certainly doable.