Since an oxygen sensor is mounted in the exhaust manifold or pipe, both of which shrink when cold, you can spend a long time trying to loosen it with your hands when the engine is cold. It is better not to endanger the sensor or the threads on which it is mounted; start the engine and let it run for connection for a few minutes and shut it down. Attention should be paid not to be burnt during the following procedure. When servicing the oxygen sensor, one must be very careful since it has a permanently attached pigtail and an electrical connector that can neither be removed nor replaced; if either is damaged, the sensor will be useless. Do not allow grease, dirt, or other foreign substances to come in contact with the electrical connector or the long slender finned section at the end of the sensor and do not use any type of cleaning solvent on the unit. These oxygen sensors are very sensitive, avoid dropping or roughly transporting them, and always fix the silicone boot in the correct manner to prevent melting or operational problems. This procedure is common to both upstream and downstream sensors the upstream sensors are fitted in the exhaust pipes immediately after the exhaust pipe flange at the cylinder head for V6 engines or exhaust manifold for V8 engines while the downstream sensors are fitted in the exhaust system after the catalytic converter. Remove the black cable from the negative terminal of the battery. On V6 models, upstream sensors must be accessed from the top of the vehicle while downstream sensors can be accessed from the bottom of the vehicle In V8 models all the sensors are accessed from the bottom of the vehicle. Except for the removal of an upstream sensor on a V6 model, lift the front of the car and place it on jackstands, and then, take off the engine under cover. Identify the location of the oxygen sensor, follow the wires of the sensor till the connector and remove it, which will remove any clips on the harness too. Locate the oxygen sensor and using a wrench or an oxygen sensor socket, unscrew the sensor, although for removal, use a slotted socket. If reinstalling the old sensor, the use of anti-seize compound at the threads will be appropriate incase one may find it hard to remove the sensor next time, for the new sensor will already have a layer of anti-seize compound on its threads. Removal is the reverse of installation, where one makes sure that the oxygen sensor is tightened to a certain torque.
