Unless it was torqued (tightened) too tightly and broken when it was installed, in operation it suffers no mechanical wear. It may simply be worn out and failed due to age.
Could be a diesel? If not then replace your oxygen sensor on your exhaust. A bad oxygen sensor causes the exhaust smoke to be dark in color.
It is caused by Bank 2 Sensor 2 oxygen sensor failing.
Newer oxygen sensors are heated for accuracy. If the heater element goes bad the oxygen sensor doesn't work and needs to be replaced. If you have an oxygen sensor heater malfunction, it just means that the oxygen sensor has failed.
They don't actually break they get dirty from dust that makes it thru your air cleaner that causes them to malfunction
The oxygen sensor is "done". It should be replaced.
causes very poor gas mileage
There is a problem with the downstream oxygen sensor. I would replace it.
There are two oxygen sensor for Mitsubishi Outlander. Front Oxygen Sensor and Rear Oxygen Sensor
If the vehicle was built with an oxygen sensor, you will need an oxygen sensor.
catalytic converter, oxygen sensor, exhaust leak
If you have a 4g63 motor a common problem is crankwalk, this will damage or break off the sensor.
Theres usually a oxygen sensor around or even inside the cat so when you remove the cat it causes codes to be sent to your computer and your check engine light will come on. That's the only effect it has on the sensor.