Because it is installed in the exhaust manifold or pipe, both of which contract when cool, an oxygen sensor might be very difficult to loosen when the engine is cold. Rather than risk damage to the sensor or its mounting threads, start and run the engine for a minute or two, then shut it off. Be careful not to burn yourself during the following procedure. Remove the key from the ignition key lock cylinder, raise the vehicle, and place it securely on jackstands. Special care must be taken whenever a sensor is serviced. Oxygen sensors have a permanently attached pigtail and an electrical connector that cannot be removed; damaging or removing the pigtail or electrical connector will render the sensor useless. Keep grease, dirt, and other contaminants away from the electrical connector and the louvered end of the sensor. Do not use cleaning solvents of any kind on an oxygen sensor, as they are extremely delicate. Avoid dropping or throwing the sensor around or handling it roughly. Ensure that the silicone boot on the sensor is installed in the correct position to prevent melting and ensure proper operation. Detach the wire harness clip and disconnect the upstream oxygen sensor electrical connector by squeezing the two locator pins together and pulling the clip out of its bracket, then depress the locking tab to disconnect the electrical connector. Remove the upstream oxygen sensor using a wrench, as there isn't room for an oxygen sensor socket. If installing the old sensor, apply anti-seize compound to the threads to facilitate future removal; for a new oxygen sensor, applying anti-seize compound is unnecessary since the threads already have it. Installation is the reverse of removal, ensuring the oxygen sensor is tightened to the specified torque. For the downstream oxygen sensor, detach the wire harness clip and disconnect the electrical connector, then remove the sensor using an oxygen sensor socket or a wrench if one is not available. Again, if installing the old sensor, apply anti-seize compound to the threads, while it is not necessary for a new sensor. Installation follows the same reverse procedure, ensuring proper torque is applied.