I have a Mazda 6 with the 2.3l I-4. I am currently getting the codes 0031, 0032, 0134. My car itself hasn't been running rough or losing gas mileage or anything, but I need to get the car inspected soon. Everywhere I have looked online referring to the location of that sensor has been conflicting (I am pretty sure it is supposed to be bay 1 sensor 1), but some websites have said its just before the cat, some say its the sensor towards the front of the car, and I also read it was below the alternator. I really don't feel like checking all of them to find the right one.

If anyone could tell me the true location for that, it would be great. thanks

 

Those codes are for the Air Fuel Sensor ( A/F) It measure the Air - Fuel ratio of the exhaust gases leaving the engine. ( Rich vs lean)

This is often mistakenly called a O2 sensor, which is wrong.

The true O2 sensor is post catalytic convertor. Its purpose is to measure the efficiency of the catalytic convertor.

The A/F sensor is the closest sensor to the engine, (upstream of the catalytic convertor)

 

thanks, I changed that one and now everything's good!