One of the many data points the onboard computer analyzes is from the Mazda Oxygen Sensor. This data is crucial for determining the correct air to fuel ratio so the engine can perform at its maximum fuel efficiency while maintaining peak output. When peering under the hood of your Mazda, the oxygen sensor can easily be seen by looking at the exhaust pipe just below the exhaust manifold. The metal protrusion with a wire connected to it in this location is the oxygen sensor. It is in this location so the reading on the oxygen in the exhaust gases being produced by your Mazda engine can be compared to the oxygen levels in the atmosphere surrounding your vehicle. You will also see one just behind your catalytic converter. The precision of the computations necessary for the Mazda engine to operate at its maximum levels is evident when you examine air/fuel corrections made by the computer as it determines oxygen levels in changing elevations. This is the reason why engine performance is not affected in a negative manner when your vehicle travels the roads in the mountains or on the plains. It is also the reason the Mazda oxygen sensor must be operating properly at all times. The indication that the oxygen sensor on your vehicle is faulty is when the check engine light is illuminated on the dash panel for the driver to see. When this occurs, a code is sent to the onboard computer informing it there is a faulty part in its system. Once the codes are retrieved, it can be determined if the faulty part is the oxygen sensor and its replacement is required for the engine to operate as it was designed to do.