Oxygen Sensor
Located in exhaust manifold, the oxygen sensor detects changes in air/fuel ratio. When beyond a narrow range which is very close to 14.7:1, maximum emission control cannot be accomplished by 3-way converter.
When heated by exhaust gases, oxygen sensor generates a voltage signal which varies with amount of oxygen sensed. At high oxygen content (lean mixture) voltage signal is low. With low oxygen (rich mixture), high voltage signal is created.
The oxygen sensor must be replaced at 30, 000 mile intervals to ensure proper operation. A mileage counter activates a warning light when the replacement interval has elapsed. A 9-volt battery supplies power to the electronic counter to prevent memory loss when the vehicle battery is disconnected. See "Maintenance" in this article .