The onboard computer reads the data from the Lexus oxygen sensor in its determination for the correct fuel to air mixture that should be used for the engine. When this sensor and any other one on your Lexus fails to function, the onboard check engine light will be illuminated on your dash panel. This is when a code is stored on your onboard computer indicating the failing of a sensor. The only purpose of the oxygen sensor on your vehicle is to determine the ratio of oxygen in the atmosphere as compared to what is present in the exhaust gases being produced by your vehicle. Most Lexus owners know this variation in oxygen is just a fraction of a percentage, but this data is one of the reasons the maximum fuel mileage and performance of your vehicle can be maintained for the lifespan of your car. The Lexus oxygen sensor is the easiest sensor to locate under the hood of your vehicle. It is the only thing on your exhaust pipe just below the exhaust manifold. The failure code will be sent to the onboard computer when the oxygen sensor fails or the wire it is connected to is broken or disconnected. The code of the failing oxygen sensor can be found in the service manual of your Lexus model. Before the oxygen sensor is replaced, the battery has to be disconnected. This will make the disconnection of this electrical component safe for the technician. It will also clear the stored code in the onboard computer so when the system is check in the future, a false reading is not present. It will also turn off the check engine light on the dash panel.