Park your car in a safe place with a level surface and plenty of room for you to work around the vehicle.
Start the engine and let it reach operating temperature; then turn the ignition Off.
Open the hood and disconnect the black, negative battery cable.
Locate the oxygen sensor following the exhaust manifold down the exhaust pipe. You should see the sensor threaded into the pipe just before it connects to the catalytic converter. On some Lexus models, it is necessary to raise the vehicle to locate and reach the sensors. Raise the left side of the vehicle using a floor jack and place a jack stand near the front tire; if you are replacing both oxygen sensors, raise the back of the car and place another jack stand near the rear tire.
Unplug the oxygen sensor's electrical connector. Push the lock tab and separate the connector from the vehicle harness. Be very careful and keep your hands and body parts away from hot exhaust system components. On some Lexus models, you may need to remove the passenger seat and lift the carpeting in order to find and unplug the sensor's connector.
Remove the sensor using a box wrench or ratchet and oxygen sensor socket. If the sensor seems hard to remove, apply penetrating oil around the sensor mounting base according to the manufacturer instructions. On some Lexus models, the sensor attaches to the exhaust pipe with a flange and two bolts or nuts; use a wrench or ratchet and socket to remove the bolts or nuts.
Apply anti-seize compound to the new sensor's threads if you are installing a screw-in type sensor. Make sure not to touch the tip of the sensor with anti-seize compound. Start the sensor into the exhaust pipe by hand first; then tighten the sensor using the box wrench or ratchet and oxygen sensor socket. If you are installing a flange type sensor, install a new gasket and set the flange and sensor in place. Thread in the flange mounting nuts or bolts and tighten with a wrench or ratchet and socket.
Plug the sensor's electrical connector. If you are replacing more than one sensor, locate the second unit at the other end of the catalytic converter and replace it following Steps 5 through 8; then lower the vehicle and connect the black, negative battery cable.