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.
The P0135 code indicates a problem with the oxygen sensor circuit for Bank 1, specifically the heater circuit of the upstream oxygen sensor. Common causes include a faulty oxygen sensor, issues with the sensor's wiring or connectors, or a malfunctioning engine control module (ECM). Additionally, problems such as blown fuses or insufficient power supply to the sensor's heater can also trigger this code. Proper diagnosis is essential to pinpoint the exact cause.
There are two oxygen sensor for Mitsubishi Outlander. Front Oxygen Sensor and Rear Oxygen Sensor
If you have a 4g63 motor a common problem is crankwalk, this will damage or break off the sensor.
catalytic converter, oxygen sensor, exhaust leak
If the vehicle was built with an oxygen sensor, you will need an oxygen sensor.