Be very careful when servicing an oxygen sensor as it has a permanently attached pigtail and electrical connector which should not be removed. Damage or removal of the pigtail or electrical connector can adversely affect operation of the sensor. Grease, dirt and other contaminants should be kept away from the electrical connector and the louvered end of the sensor. Do not use cleaning solvents of any kind on the oxygen sensor and do not drop or roughly handle the sensor. The silicone boot must be installed in the correct position to prevent the boot from being melted and to allow the sensor to operate properly. For replacement of upstream oxygen sensors, locate the electrical connector and disconnect it. Detach the sensor wiring harness from any clips. Unscrew the sensor with an oxygen sensor socket if one is available. You may have to raise the vehicle and support it securely on jackstands to reach it. If you're going to install the old sensor, apply anti-seize compound to the threads to ease future removal. If you're installing a new sensor, the threads will already have anti-seize on them. Installation is the reverse of removal. Tighten the sensor securely. For downstream oxygen sensors, raise the vehicle and support it securely on jackstands. The downstream oxygen sensors are accessible only from underneath. Disconnect the wiring harness from the pigtail of the sensor. Unscrew the sensor, using an oxygen sensor socket if one is available. If you're going to install the old sensor, apply anti-seize compound to the threads to ease future removal. If you're installing a new sensor, the threads will already have anti-seize on them. Installation is the reverse of removal. Tighten the sensor securely.