What are the functions of the front and rear oxygen sensors?
2 Answers
Function of the front oxygen sensor: The front oxygen sensor primarily detects the oxygen concentration in the engine exhaust gases and provides this information to the ECU in the form of an electrical signal. Based on the oxygen concentration in the exhaust, the ECU performs closed-loop control of the fuel injection quantity. If the oxygen concentration in the exhaust is too high, it indicates that the engine's air-fuel mixture is too lean. Conversely, if the detected oxygen concentration is too low, it means the mixture is too rich. This information is used to adjust the fuel injection quantity. Function of the rear oxygen sensor: The rear oxygen sensor mainly detects the oxygen concentration in the exhaust after it has been purified by the catalytic converter. Automotive oxygen sensors are divided into front and rear oxygen sensors, with the main differences being their installation positions, functions, and impacts. The front oxygen sensor is typically located behind the exhaust manifold, while the rear oxygen sensor is usually positioned after the catalytic converter. Working principle of the oxygen sensor: The oxygen sensor operates based on the Nernst principle. Its core component is a porous ZrO2 ceramic tube, which is a solid electrolyte. Porous platinum (Pt) electrodes are sintered on both sides of the tube. At a certain temperature, due to the difference in oxygen concentration on both sides, oxygen molecules on the high-concentration side (inside the ceramic tube) are adsorbed onto the platinum electrode and combine with electrons (4e) to form oxygen ions (O2-), making this electrode positively charged. The O2- ions migrate through oxygen ion vacancies in the electrolyte to the low-oxygen-concentration side (exhaust side), making that electrode negatively charged, thus creating a potential difference. Functions of the oxygen sensor: To reduce engine exhaust pollution and ensure that the catalytic converter achieves maximum conversion efficiency for hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust, thereby maximizing the conversion and purification of emission pollutants. In engines equipped with catalytic converters to reduce exhaust pollution, the oxygen sensor is an essential component. The oxygen sensor measures whether there is excess oxygen in the engine's post-combustion exhaust, i.e., the oxygen content, and converts this information into a voltage signal sent to the engine computer, enabling the engine to achieve closed-loop control based on the target air-fuel ratio.
These front and rear oxygen sensors are actually little devices installed on the exhaust pipe. After driving for so many years, I find them extremely important. The front oxygen sensor is located before the main catalytic converter, monitoring the oxygen content in the engine's exhaust gases and telling the car's computer how much fuel to inject, ensuring the combustion is just right—not too much, not too little. The rear oxygen sensor is positioned after the catalytic converter, specifically checking how well the converter is working to ensure harmful gases are eliminated. If these sensors malfunction, fuel consumption can suddenly spike, emissions exceed standards, and the car may emit black smoke. I once experienced a faulty front oxygen sensor, and the car felt sluggish with poor acceleration. Regular checks can save a lot on fuel costs and reduce pollution. I recommend car owners not overlook this, especially since environmental regulations are becoming stricter nowadays.
