Every Jaguar manufactured after 1980 has an oxygen sensor in it.  The Jaguar oxygen sensor is an intricate part of your emissions control system.  Important data is sent by the oxygen sensor to the engine's management control system.  Your oxygen sensor keeps your emissions low and your engine running efficiently.  In every vehicle, there is a ratio of air and fuel that must be met and maintained for your engine to perform as expected.  If the ratio is imbalanced with too much air or too little air, your vehicles performance will suffer.  When the ratio of air and fuel is not where it should be, the oxygen sensor notifies the engine's management computer by sending the data to it.  There, the engines computer will adjust the fuel output so that the ratio can be balanced back out.  Many people will experience oxygen sensor failure at one time or another.  Signs that your oxygen sensor has failed are hesitation, surging, poor acceleration, emission test failure, and poor engine performance.