Be cautious when servicing an oxygen sensor since it has a permanently attached pigtail and electrical connector that should not be removed. Removing the pigtail or electrical connector can make the sensor to stop functioning properly. Stay away from dirt and grease on the louvered end of the sensor and electrical connector. Avoid using any cleaning solvents on the oxygen sensor. It is not recommended that you drop or mishandle it roughly. The silicone boot needs to be placed rightly so as to prevent melting and also allow for proper operation of the sensor. Locate the electrical connector and disconnect it in order to replace an upstream oxygen sensor. Separate the clips from which the sensor wiring harness is hung. In case you have an oxygen socket, unscrew it using one. You will possibly have to lift up the vehicle securely with jackstands so as reach it properly. If reinstalling old sensors, put anti-seize compounds on threads for easier removal at a future date. Anti-seize is already present on new sensors' threads before installation though. The installation process is just undoing everything that was done when removing something. Tighten down firmly by hand again for safety reasons. To install a downstream oxygen sensor: raise your car, secure it using jack stands; disconnect wiring harness from pigtail of this sensor; unscrew with an oxygen socket if available; For installing old sensors only, apply anti-seize compound to threads for easy removal later; New ones always come with anti-seize on their threads, so don't add more of this; Installation part reverses everything that had been done during un-installation hence tighten hand tight again for security purposes.