O2 Sensors for Automotive Exhausts

Having an accurate air/fuel mixture will maximize engine performance, increasing horsepower across the entire RPM range. It will also result in a smoother idle, better fuel mileage, and improved acceleration. Over time, oxygen sensors collect carbon deposits and buildup, resulting in less-accurate readings and degraded performance. Replacing them (as cleaning will cause damage) when the manufacturer specifies (typically between 60,000 to 90,000 miles) will help keep engine performance optimized.

Using an air/fuel gauge and O2 exhaust sensor on your carbureted engine allows you to know if you need to change jets to increase or decrease the amount of fuel in your carburetor. This will provide you with a better idle air, part-throttle, and wide-open throttle mixture.

Oxygen (or "O2") sensors measure the amount of oxygen in the exhaust stream by threading into a welded bung fitting in the exhaust once it leaves the engine. In fuel-injected systems, the information an O2 sensor collects is fed to a computer, which will monitor and make constant changes to the amount of fuel injected into the engine. This results in the best performance, efficiency, emissions, and fuel mileage. In most applications, the oxygen sensor begins to collect air/fuel mixture data around 600-650 degrees Fahrenheit. The tip of the oxygen sensor is designed with a ceramic bulb containing platinum layers, which are permeable (allows heat and air to vent through). The inside of the oxygen sensor tip is vented through the sensor to the outside atmosphere. When the ceramic tip is exposed to hot exhaust gasses, the difference in oxygen levels between the sensor bulb tip and the outside atmosphere within the sensor body creates voltage by design. If the engine and exhaust stream is running rich, the sensor will send a signal to the computer around .8-1 volt) and a lean condition will result in a smaller voltage amount, around 0.1 volts. This info is then calculated by the computer to determine the correct amount of fuel to achieve the best ratio. Most oxygen sensors are heated to help them reach the proper temperature for a correct reading of oxygen in the exhaust.

Carbureted vehicles that did not have computers from the factory (1980 and older for most applications) do not have an oxygen sensor. From 1981 to 1995, most applications have at least one O2 sensor. From 1996 to present, all vehicles are required to have an oxygen sensor both upstream (before the catalytic converter inlet) and downstream (after catalytic converter outlet). V6 and V8 engines with dual exhaust systems require four oxygen sensors, with one on each bank of the engine both upstream and downstream.

Automotive oxygen sensor prices can range anywhere from under $20 each to over $400 each, depending on the year, make, model, and engine of the application.

On computer-controlled vehicles, when an oxygen exhaust sensor fails, the computer will create a trouble code and turn on the check engine light. Common symptoms of O2 sensor failure include rough idle, lower fuel mileage, engine stumbling and hesitation, slower acceleration, as well as lean or rich running (black smoke from the exhaust from too much fuel).

Testing the voltage with either a scan tool live data option or multimeter reading given by O2 sensors will help with determining if they are working correctly or not. Depending on the application, the voltage reading will change, so referring to the vehicle repair or shop manual will provide the correct reading and test procedure. However, in most cases, the upstream sensor should generate between .1 (lean) to .9 (rich) volts to confirm a correctly working component. The downstream exhaust oxygen sensor in most cases should read approximately .5 volts, again, depending on manufacturer's precision settings.