The check engine light will illuminate if you have a bad O2 sensor. The code set will lead you to the faulty sensor.
They generally set a trouble code and the check engine light illuminates.
exaust leaks , faster if its before the 02 sensor
If it is bad the check engine light will come on and set a code for that particular sensor.
If your car has OBD2(96 and newer) they will hook up a code reader. If you do have a bad O2 sensor the scanner can tell which one is bad. Most v6 and v8 engine have 4 sensors.
How can you tell if a crank sensor has gone bad on a 1994 Nissan altima
You have a bad 02 sensor after the catalytic converter.
engine will stall out and run very bad.
When a O2 sensor goes bad the check engine light will illuminate. The code set in the ecm will lead you to which O2 sensor is bad.
A computer diagnostic test will generally tell you if you have a faulty crankshaft position sensor.
poor gas mileage
An auto xray scanner can determine if a O2 sensor is bad.