How to correctly distinguish the faults of Volkswagen's air flowmeter and oxygen sensor? I believe that you will often encounter such problems in the practice of maintaining electronically controlled engines. For example, when reading the fault code, it is the fault code of the air flowmeter. When reading the data flow, you find that the data read by the air flowmeter is normal, but the data flow of the oxygen sensor is not within the normal range. When reading the fault code, it is the fault code of the oxygen sensor. When reading the data stream in this area, you find that the oxygen sensor is normal. However, the data flow of the air flowmeter is not within the normal range. In the above two cases, the oxygen sensor or air flowmeter can be restored to normal by replacing it alone, but sometimes it is necessary to replace them all. Cautious people don't know which one to replace is more reliable than the data stream of the decoder. The data stream is dominant, and it is best to check the waveform with an oscilloscope. I think no matter what kind of fault code appears, it depends on the data flow. If the data is incorrect, check whether it is broken or caused by other places. When the hot-wire air flowmeter is normal, the idle output voltage exceeds 1.25- 1.35 V, and it exceeds 4V when the throttle valve is fully open. The output voltage at full deceleration should be slightly lower than that at idle speed. Note: the output voltage of different models will vary greatly, and whether it is in the range at idle speed is also a way to judge the quality of air flowmeter. Almost all digital air flow meters generate varying frequency signals. The amplitude of most pulses is above 5V, depending on whether the shapes are consistent or not, and whether the angles and vertical sides of the rectangle are consistent or not. Carmen vortex street air flowmeter is an exception of digital air flowmeter, which not only increases its frequency, but also changes its pulse width during acceleration. In most cases, the amplitude of the waveform should be above 5V, and the correct shape of the waveform, the square angle and the vertical edge of the rectangular pulse should be checked according to the principle of consistency. The frequency generated at a stable air flow rate should also be stable. Incorrect key parameters are shorter pulse width, and there should be no peaks and rounded corners. Generally speaking, data flow can be used as the basis. We only need to be familiar with the data of various working conditions, and then analyze that the range of maintenance data given by the public is too large. Many sensor tests are within the data range, but they are not good. We should always measure some data in the car and save it. Some data on the decoder is converted. We can't all believe it. We'd better go to the terminal and test it ourselves.