The signal from the Nissan oxygen sensor allows for the onboard computer to make the correct computation on the air and fuel mixture each cylinder will then receive. The data being sent is the ratio of the oxygen levels of the exhaust gases to what is in the air surround the vehicle. It is true that the difference in the variations of oxygen in the atmosphere is very small; however it still does matter in this precise calculation. This is the level of precision in which the modern Nissan engine is designed to operate under, and is why the increased fuel mileage can be achieved while at the same time performance is maximized. It is also why the oxygen sensor on your vehicle must be in operational status at all times. When the Nissan oxygen sensor is either unplugged or malfunctioning, the onboard computer senses this condition and informs the driver by illuminating the check engine light on the dashboard. This illumination of the check engine light occurs not only when the oxygen sensor malfunctions but when any sensor is malfunctioning. To know just which sensor is not functioning properly, the codes in the onboard computer on your Nissan must be retrieved. Once the codes are retrieved and the faulty oxygen sensor has been identified, it can be replaced with the simple use of a hand wrench. Before that procedure is undertaken, the battery should be disconnected. This will prevent an electrical shock or short from occurring during this procedure. It will also clear the code referring to a faulty oxygen sensor along with any other code the onboard computer has stored in its memory. You will also want to wait for your exhaust pipes to cool down to prevent any burning. With the new sensor in place your Nissan engine will then be able to perform at its maximum potential once again.