During repair or replacement of oxygen sensor, care must be taken especially because the oxygen sensor is fixed in the exhaust manifold or exhaust pipe and can be very tight to loosen when cold; you can turn the engine on for some ten to fifteen minutes before loosening the sensor or its holding nuts. Oxygen sensors have a pigtail that is an electrical connector that should not be damaged and should be left always installed; it is averse to having grease, dirt, and other contaminants get to the electrical connector and the louvered end of the sensor. Organic solvents should not be applied on an oxygen sensor, which is rather sensitive and should be handled gently, and not dropped. Check that the silicone boot covering the sensor is positioned in a manner that will not melt and cause problems when the sensors are operating. For the upper part of the engine compartment, the upstream oxygen sensors require the removal of the engine cover, the disconnection of the electrical connector, and unclipping the connector before the removal of the sensor. If it is to reinstall the old sensor apply anti seize compound on the threads while new sensors come with it pre-applied. Downstream oxygen sensors usually lie beneath the car or at the lower end of the catalytic converter on later V6 models or years On early models, raise the car securely, find the sensor, and disconnect the electrical connector and any wiring bracket that may exist. In the subsequent models of V6, the left transaxle mount may require to be removed in order to gain access. Disconnect the downstream sensor, if reinstalling the original sensor, apply anti seize as required, reverse the procedure under installation and tighten the sensor properly.