August 10, 2022

load cell fault diagnosis and maintenance technology

  1. Diagnose by voltage signal. Before testing the oxygen load cell, the engine must be within the normal operating temperature range.


As for the diagnosis method, I won’t repeat it here, I believe you are already familiar with it. When the engine is idling and the temperature is normal, if the air-fuel ratio slightly deviates from the theoretical air-fuel ratio, the output voltage of the oxygen load cell will change periodically from low pressure to high pressure. The output voltage of a typical oxygen load cell changes periodically from 0.3V to 0.8V.


2. Some advices for load cell fault diagnosis and maintenance technology measurement.


A-You must use a digital voltmeter to test the oxygen load cell. Many materials have introduced that if you use other types of low impedance multimeters to damage the oxygen load cell, but in actual work, the reason why I mentioned that the digital meter is not based on the introduction of the data , But out of actual work needs.


Everyone knows that the precise indication range of an analog multimeter is within the middle range of its dial, but the oxygen load cell voltage signal range we tested is exactly the opposite of the precise indication range of an analog multimeter. Its maximum and minimum values ​​are in the multimeter. Therefore, if you use an analog multimeter to test the voltage signal of the oxygen load cell, it is not accurate at all. This is the reason why I choose a digital multimeter.


B-If the oxygen load cell in the exhaust pipe is contaminated and cannot be in contact with oxygen, it may give a continuous high voltage signal


C-Do not use sealant as much as possible when replacing the oxygen load cell. The reason is that if too much sealant is applied, the sealant will burn due to high temperature when the engine is working, and the burning waste of the sealant will let you in a short time. The newly replaced oxygen load cell is rapidly aging and failing, but you can’t find out where the problem is inexplicably.


3. During the measurement, A-If the voltmeter continues to read a high voltage, it indicates that the air-fuel ratio may be too rich, or the load cell may be contaminated. B-Voltometer reading continues to low voltage, indicating that the air-fuel ratio may be too high, or the load cell is faulty. C-If the voltage signal of the oxygen load cell remains at an intermediate value, it may be that the computer loop is blocked or the load cell is damaged.


4. Some explanations about the voltage signal of the oxygen load cell:


In most cases, when we detect the oxygen load cell, our maintenance personnel will let the engine work for several minutes to ten minutes in advance, let the engine enter the closed-loop working state, and measure whether the voltage signal output by the oxygen load cell changes between high and low. There is nothing wrong with this approach, but can you tell us the reason for asking you to do this? I have met many repairmen in their understanding that the oxygen load cell will produce a voltage signal that changes with the increase of the engine’s operating temperature. If the output voltage signal remains basically the same, it is a basically stable constant value. The oxygen load cell has been damaged. In fact, this is a mistake in understanding the oxygen load cell. In fact, the change of the voltage signal of the oxygen load cell is determined by the change of the oxygen content in the exhaust gas discharged by the engine. The size of the engine load and the different operating conditions directly lead to the difference in the oxygen content of the engine exhaust. The voltage signal of the oxygen load cell will naturally change with the change of the oxygen content. Therefore, the voltage signal of the oxygen load cell changes because of the influence of the engine’s working conditions. Try to think about it, if for some reason the engine is always in a rich state, or the state of the mixed gas is too high, what will happen to the oxygen load cell? There are two answers-(1) always output a high voltage signal, (2) always output a low voltage signal, but this does not mean that the oxygen load cell is damaged.


5. Errors in diagnosis ideas


In the actual maintenance work, the engine is not in good working condition, such as unstable idling, black smoke from the idling engine, insufficient power and many other faults. During the inspection process, we will read the fault code of the engine control computer. Sometimes there will be information that the oxygen load cell has been damaged. We cleared the code and read the current fault code randomly after a period of road test. It was found that other fault codes did not appear but the fault information that the oxygen load cell was damaged still exists. Then perform the performance test of the oxygen load cell, it is confirmed that it is really damaged, and it will be updated without hesitation.

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