O2 sensors, also called lambda sensors or oxygen sensors, measure the proportion of oxygen in vehicle exhaust. The sensors were first installed in vehicles in the 1970s, when the Environmental Protection Agency introduced exhaust regulations. Later, vehicle manufacturers began to install two sets of sensors: one before the catalytic converter, and one after. Physically, there's no difference between front and back O2 sensors. They function in the same way, but the vehicle's computer uses the measurements that they take for different purposes.
How an O2 Sensor Works
The first step in the invention of the O2 sensor occurred in Germany in 1899, when Walter Nernst devised the Nernst cell. At temperatures higher than 620 degrees Fahrenheit, the ceramic cell was capable of transferring oxygen ions from the gas inside of the cell to outside gases, generating an electrical current whose magnitude was dependent on the difference in the oxygen concentration of the two gases. In 1976, the Bosch company adapted the Nernst cell for use in automobiles.
Modern vehicle O2 sensors work according to the same principles that the original Nernst cells did. A zirconia bulb lined with platinum facilitates the transfer of the oxygen ions between air inside the sensor and the exhaust gases that flow over it at temperatures higher than 600 degrees Fahrenheit. Most O2 sensors have an internal heating element so that they can reach the required temperature more quickly and remain there even during idling, when exhaust temperatures can drop below the threshold for oxygen sensor function.
The Purpose of a Front O2 Sensor
Front O2 sensors analyze the exhaust coming directly from the engine. When O2 sensors were installed only in one place, they were located in the position that made them what would be called front O2 sensors today. They communicate with the engine control module, the computer that controls the mixture of fuel and air that goes into the engine. If the mixture is too rich, which means that it contains too much fuel, then the computer reduces the fuel in the mixture that goes into the engine; if the exhaust is too lean, then the computer adds more fuel to the mix. The computer tries to maintain an ideal ratio of air to fuel to minimize emissions and improve fuel economy.
The Purpose of a Back O2 Sensor
Back O2 sensors are located after the catalytic converter, a part that facilitates the conversion of pollutants in the exhaust to harmless by-products. These sensors monitor the efficiency of the converter. The computer compares the exhaust that flows into the converter with the exhaust that comes out. If the effect that the converter has on the composition of the exhaust decreases, it means that the converter is wearing out. The computer can monitor the level of the converter's operation and alert the driver when the converter needs to be replaced.
- Keith Kiowski; Mechanic; Las Vegas, NV
- European Car Magazine: A History of the Oxygen Sensor
- AutoHauzAZ: Oxygen Sensors & Emissions --- Facts & Repair Advice
- Photo Credit exhaust fulmes image by bilderbox from Fotolia.com
What Are the Differences Between a Mac & PC?
The term "personal computer," or PC, came into use in the early 1970s, referring to any microcomputer, as opposed to a mainframe....
Ford F250 Problems
The Ford F-250 belongs to the popular F-Series pick-up truck line-up manufactured since 1948. Initially, apart from its size (it traditionally weighs...
The Difference Between Narrow Band and Wide Band Oxygen Sensors
The oxygen sensor is one of the most important advancements in modern vehicles. Without it, we would not only waste gas, but...
Difference Between Upstream & Downstream Oxygen Sensors
All post-1996 vehicles have a lot of emissions equipment, including oxygen sensors. Most emission-controlled cars have two to four oxygen sensors, depending...
How to Change the Oxygen Sensor on a Chevy Cavalier
The common engine in the Chevy Cavalier is the 2.2 liter four cylinder. A few models have a 2.4 liter engine. Both...
How to Bypass the Rear O2 Sensor
The O2 sensor in your vehicle gathers information about the emissions that are being put out by your vehicle. This information is...
How to Replace Sequoia Oxygen Sensors
Oxygen sensors measure the amount of oxygen in your car's fuel system when considered in conjunction with other components. The sensors are...
How to Replace the Coolant Temperature Sensor in a 2002 Audi A6
The coolant sensor on the 2002 Audi A6 is an important component in the controlling of the engine temperature in order to...
Differences Between the Mercedes E320 and E350
The E-class of Mercedes Benz vehicles was first released to consumers for the 1994 model year with a nameplate and design that...
Differences Between IR Sensors & RF Sensors
Infrared (IR) sensors and radio-frequency (RF) sensors both contribute to keeping our homes smart, but their methods and effects vary considerably. IF...