How to Replace Volvo O2 Sensor

1. Raise the car with the floor jack and place jack stands under the frame for safety. Lower the car onto the jack stands.
2. Disconnect the electrical connector to whichever oxygen sensor you're replacing. The sensor has a short electrical harness extending from it with a connector. Pull the connector apart to disconnect it from the main harness. Turn the oxygen sensor counterclockwise using the 7/8-inch wrench to remove it.
3. Remove the plastic cover over the lower part of the new sensor and thread it into the hole vacated by the old sensor. Turn it clockwise as far as possible by hand and continue to tighten with the wrench.
4. Connect the sensor's electrical connector to the main harness connector by pushing it in until it clicks in place. Remove the jack stands and lower the car.