The oxygen sensor is a part of your emissions control system that allows your engine to perform at its best while producing as few emissions as possible.  If you're driving a Fiat manufactured after 1980, your vehicle has an oxygen sensor.  Every vehicle has a specific oxygen to fuel ratio that is considered perfect for optimal performance.  Your Fiat oxygen sensor helps to keep this ratio in check by sending the information to your engine's computer.  If you've got too much air in the ratio, you've got a lean air mixture.  If you have too little air in the ratio, it's called a rich mixture.  Either way, when your Ferrari oxygen sensor is working properly it will catch these imbalanced ratios and send the data to the engine computer.  The engine's computer will then make adjustments to the fuel output so that the mixture is balanced once again.  A broken oxygen sensor can result in hesitation, surging, poor acceleration, emissions test failure, and poor engine performance.
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