Particular caution needed when working on an oxygen sensor or air/fuel ratio sensor because the pigtail and electrical connector are always integrated; if they are damaged the sensor must be replaced. The electrical connector and the louvered end of the sensor must not be greased, must not accumulate dirt and other contaminants and only mild detergents must be used while cleaning these sensors. Furthermore, do not drop the sensors or handle them roughly, also make sure the blue silicone boot is properly fixed in place so it will not melt and so that the sensor works properly. For replacement, know that the nut on an oxygen sensor may seize up when the engine is cold, so one has to start the engine for a while. First of all ensure you have separated the wire from the negative terminal and then safely lifted the car on jackstands. The upstream oxygen sensor is mounted on top of the exhaust manifold and can be removed by pulling on the electrical connector and loosening the sensor with a unique socket and if the old sensor is being reinstalled the threads of the sensor bore should be cleaned and the sensor threads should be coated in anti seize compound and this obviously does not apply to new sensors. The downstream oxygen sensor procedure is the same to the upstream oxygen sensor that is on the left side of the top of
Catalytic Converter, and that involves removing and disconnecting the electrical lead, removing the sensor, and then cleaning the threads of the sensor; if you are reusing the old sensor apply anti-seize compound before putting the sensor in. Lasty, add the downstream sensor and make sure that it is properly fixed by tightening it, proceeding in the reverse sequence.