The Toyota FJ Cruiser oxygen sensor analyzes the exhaust fumes and deposits produced by the engine. If the air fuel ratio is too lean or not enough, the oxygen sensor sends feedbacks to the vehicle's ECU system. The oxygen sensor's role is to effectively control emissions for better engine performance and increase fuel economy. The location of the Toyota FJ Cruiser O2 sensor is toward the rear of the vehicle either prior or after the catalytic converter. Heated sensor lifetime is 100,000 miles while unheated is 50,000 miles. Common symptoms of a faulty oxygen sensor are unstable idling speeds and sudden drop in gas mileage.