There are two oxygen sensors on the car, one behind the exhaust manifold and the other behind the three-way catalyst. We are accustomed to calling it a front oxygen sensor and a rear oxygen sensor.
Front oxygen sensing
The front oxygen sensor, also known as the air-fuel ratio sensor, provides a signal to the ECU to correct the fuel injection amount. Located behind the exhaust manifold, the exhaust gas after combustion of the cylinder reaches the front oxygen sensor. When the gasoline engine is working, the ECU uses the air flow meter and the intake pressure sensor to comprehensively determine the intake air amount. However, the intake air quantity control must have an error. How to verify whether the air-fuel ratio is normal? That is, to detect the oxygen concentration in the exhaust gas, if the oxygen concentration is too high. It shows that there is too little gasoline and no oxygen is completely consumed. If the oxygen concentration in the exhaust gas is too low, the injection is too much and the oxygen is not enough. The ECU relies on the signal from the front oxygen sensor to correct the amount of fuel injected. The picture above shows the front oxygen sensor. Generally, we can open the hood and see it on the side of the exhaust pipe.
Rear oxygen sensor
The post-oxygen sensor is used to judge the purification effect of the three-way catalyst. Because the exhaust gas enters the three-way catalytic converter, the harmful substances in the exhaust gas will be catalytically oxidized to harmless substances at high temperature. This process needs to consume a certain amount of oxygen, so the oxygen concentration will decrease after the exhaust gas passes through the three-way catalyst, if the oxygen sensor detects The oxygen concentration is less than the data detected by the front oxygen sensor, which indicates that the three-way catalyst is working properly. If the data of the front and rear oxygen sensors are the same, it means that the three-way catalytic converter does not play the role of purifying the exhaust gas, and the engine fault light will be illuminated at this time.
It is often said that the car is fuel-free and the oxygen sensor is replaced. In fact, this is a very one-sided statement. First of all, there are many reasons for fuel consumption, not just the problem of oxygen sensors. Secondly, the service life of the oxygen sensor itself is very long, and it is easy to be easily damaged. The common oxygen sensor failure is mainly pollution. For example, if the silicon content in the gasoline exceeds the standard, white deposits on the surface of the oxygen sensor are generated, and the ferrocene antiknock agent is used. Gasoline will cause red deposits on the surface of the oxygen sensor. If the engine is not well burned, it will produce black carbon deposit on the surface of the oxygen sensor. When the ECU thinks that the oxygen sensor signal is abnormal, the oxygen sensor signal will not be adopted. In order to ensure that the dynamic fuel injection will be biased. Thick, so fuel consumption will increase. However, the engine fault light will be on at this time. This usually only needs to be cleaned.
In addition, in order to measure the discharge flow of automobile exhaust gas, an ultrasonic gas flow sensor can also be used.