Fault case of air flow meter | Yusheng S350 reads fault code and shows abnormal air flow. After replacing the air flow meter and clearing the fault light, it suddenly reverses ..

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1. Fault analysis of air flow meter

Fault 1: Audi A6, APS type engine has unstable idle, black smoke under local load, and sometimes stalls when shifting gears. Detection process: The internal fault of the computer is stored as an old air flow meter fault, but after a detailed inspection of the air flow meter circuit, the condition is normal, and using VAG1552 to execute functions 01-08 reads data quickly. The intake air volume at idle is 2.5g/s, which meets the specifications. But the problem with the air flow meter remains the same after replacing it, the cold car works normally after replacing the computer, and the problem persists after heating up the car. At this point, when checking the entire vehicle data block again, it was found that the voltage transition frequency of the oxygen sensor in the second zone of the 7th group in the 08 data group was slow. The normal conversion rate is 20-30 times per minute, while this car only needs 5-6 times uniformly, indicating that there is a problem with the oxygen sensor. Repair consequence: Replace the oxygen sensor and clean up the problem. Problem analysis: This problem is caused by the contradiction between the air flow meter flag signal and the oxygen sensor flag signal displayed in the computer. In practice, it is due to the oxygen sensor being misaligned, resulting in mismediation. However, in terms of consequences, it is the same as the severe deviation of the air flow meter flag signal, which causes the oxygen sensor to be unable to adjust. Here, the computer prioritizes the main signal, which is the air flow meter signal. As long as we can accurately understand the fault reminders of the computer, the problem will not be difficult to handle. This problem

can be understood as: related to air flow meters, we easily think of oxygen sensors, which requires us to investigate their principles more and deal with divergent situations. Problem 2: The Audi A6 and 1.8T engines have unstable idle, weak driving, and emit black smoke. Make a fundamental setup and clean up the problems, but after a few days, it shows a repetition. Detection process: The computer displays a temporary malfunction of the air flow meter. The malfunction persists even after replacing the air flow meter and the computer, and the entire vehicle data block is checked to be normal. However, a detailed inspection of the air flow meter circuit revealed that the resistance value of the signal line at the intake end of the air flow meter was too high, with a normal value of 0.5 ohms and a practical value of 3.6 ohms. The real cause of the problem is that there is a loose connection in the circuit. Resetting the harness plug cleared the problem. Problem analysis: This kind of problem belongs to extraordinary problems, but in practical maintenance, it often encounters false positives. And it is relatively difficult to handle. We can find a problem here, that the air flow meter flag signal line is located at the corner of the plug, which easily leads to position problems and poor contact during the production process. Among other plugs, the relative position is also worth noting. In addition, as a crucial component, the air flow meter has a very low failure rate. When the computer reminds us of its problems, we should take it seriously. Problem 3: The Audi A6 and 1.8T have no cooling air when the air conditioning is turned on, and the engine is idling when in gear. Testing process: First, inspect the air conditioning

Fault case of air flow meter | Yusheng S350 reads fault code and shows abnormal air flow. After replacing the air flow meter and clearing the fault light, it suddenly reverses ..

1. Fault analysis of air flow meter

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