You already know that your car’s engine is responsible for creating the energy that turns your wheels and propels your vehicle down the road. It generates this energy through its combustion process. Air and fuel enter each cylinder’s combustion chamber where the mixture is compressed and ignited. A lot of drivers fail to realize that the mixture within each cylinder’s chamber must be carefully measured. The oxygen sensor (OS) plays an important role in ensuring an optimum ratio between the air and fuel.
Below, we’ll explore this component, and the job it performs, in greater detail. You’ll learn how the OS is part of your engine’s feedback loop. I’ll also describe how it works and what can happen if it fails.
Maintaining The Perfect Ratio
The optimum ratio between the oxygen and fuel that enters your engine’s combustion chambers is 14.7 to 1. Too little air causes a rich mixture. In such cases, the combustion process results in unburned fuel that flows out of the chamber and into the exhaust system. That generates pollution and will cause your vehicle to fail an emissions test.
When there is too much air in the combustion chamber, a lean mixture results. That produces excess nitrogen oxides, a dangerous pollutant. Not only does that make your car’s catalytic converter work harder, but it can also lead to engine damage.
Maintaining the optimum ratio between the air and fuel mixture requires constant monitoring. That is the job of your oxygen sensor.
Understanding The Control Loop
The OS sits within your vehicle’s exhaust pipe and measures whether the air-fuel mixture is too lean or too rich. It accomplishes this task by identifying the amount of oxygen present in the exhaust leaving each cylinder’s combustion chamber. It sends a continuous stream of data to your car’s computer.
The computer receives the data sent from the O2 sensor and uses it to modify the ratio of air and fuel used during combustion. If the oxygen sensor notes a too-lean or too-rich mixture in the exhaust, the computer (i.e. the engine control unit, or ECU) will adjust the fuel intake system in order to compensate.
Any modifications made by your car’s ECU will produce changes in the oxygen level present in the exhaust. These changes are identified by the OS, which continues sending a stream of corresponding data to the ECU. This is a closed feedback loop.
How The Oxygen Sensor Performs Its Job
Your vehicle’s O2 sensor generates a small electrical current when the component becomes heated. This voltage is produced by a chemical reaction. The portion of the sensor that is screwed into the exhaust manifold is equipped with a small bulb. The bulb is coated with chemicals that produce a reaction when they are exposed to the gases contained in the exhaust leaving your car’s combustion chambers.
The voltage created by this chemical reaction communicates the level of oxygen to the engine control unit. A high voltage means the mixture is too rich. A low voltage means the mixture is too lean.
When The Component Fails
Oxygen sensors can last up to 80,000 miles, but can fail earlier depending on your driving habits. If it fails, your car’s computer will be unable to make changes to the ratio of the air-fuel mixture used in your engine’s combustion chambers. In effect, the closed feedback loop that normally ensures the mixture is optimized, opens. Your emissions will rise, potentially causing your vehicle to fail an emissions test. Your gas mileage will fall as your engine becomes less efficient. You might also notice a reduction in performance as the air-fuel mixture runs rich or lean.
If your car’s O2 sensor fails, have an OEM-certified replacement installed as soon as possible. Otherwise, your engine may begin experiencing problems that worsen with time.
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