Troubleshooting of braking system caused by dirty

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Troubleshooting of brake system caused by dirty brake fluid (I)

with the rapid development of automotive industry As well as the continuous improvement of the requirements for vehicle driving performance, people pay more and more attention to the safety of vehicles. Automobile anti lock braking system, referred to as abs Due to the use of electronically controlled anti lock system, the longitudinal direction of the wheel can be at the peak of the adhesion coefficient in the process of vehicle braking At the same time, it also maintains a high coefficient of adhesion on the side, so that the car has good anti side slip ability and the shortest braking distance To improve the safety of vehicle driving. Therefore, ABS devices are increasingly equipped on modern car class 1 vehicles. When the ABS device is working, the friction heat generated by the braking system is higher than that of the vehicle without ABS device Deterioration of brake fluid will also occur relatively early If you continue to use the brake fluid when it deteriorates, it will affect or even damage the normal operation of the brake master cylinder, wheel cylinder, hydraulic control unit and other components, reducing the braking efficiency and even braking failure Cause potential accidents and affect the safety of drivers and passengers. Therefore For the brake fluid of vehicles equipped with ABS device, strictly follow the replacement cycle and brand label recommended by the automobile manufacturer, and replace the brake fluid on time. In addition, according to the specific conditions of use Replace it in advance if necessary. Some drivers think the braking effect is good, so there is no need to replace it. They don't go to repair and replace it until the braking effect is bad or there is a fault. As everyone knows, it will be more troublesome to repair when there are fault symptoms. If an accident occurs because of this, it will be more than worth the loss. Therefore, to change this wrong understanding, we must not try to save trouble and miss major events. The following are two examples of brake system failure caused by failure to change the brake fluid as required in my actual work

example 1

fault phenomenon: a Santana 2000GSi (superman of the times) car The mileage is 11ooookm. The braking effect of the car is good during normal driving. The ABS system works normally during emergency braking. But sometimes when the vehicle is stationary, the brake pedal begins to sink to the bottom after continuously pressing the brake pedal for about 5S. At this time, release the brake pedal, and then step on it again, and you will step on it to the bottom, which makes you feel like stepping on the clutch. If you release the brake pedal, stop for a while and press it again, it will return to normal. According to the car owner This phenomenon has existed for a long time It just happened once in a while at the beginning, and it was normal after a slow step. I checked elsewhere and found nothing wrong. But later, this fault phenomenon became more and more obvious and frequent, especially when waiting for the red light, and my heart was getting worse and worse


after receiving the car, first check each sub pump and connecting pipeline, and no trace of leakage is found. According to the analysis of previous experience, it is possible that the abnormal pressure relief of the piston and leather cup of the brake master cylinder may cause the pedal to slide. However, when stepping on the brake pedal, check the brake fluid in the master cylinder reservoir, and there is no obvious oil return, but the brake fluid is dirty. To be on the safe side, replace the brake master cylinder and brake fluid, and then test run The fault phenomenon has been alleviated and appears less frequently But it still exists. Is there a problem with the ABS control unit? Connect the fault diagnosis V.A.G1552 and enter the ABS system. No fault code is found after checking. At this time, it is mainly suspected that this fault is caused by the lax closing of the normally closed valve in the ABS hydraulic controller. Therefore, the solenoid valve in the ABS control unit is diagnosed and tested by using the actuator diagnostic function of v.a.g. 1552, which will produce harmful materials such as dioxin (the specific operation steps and diagnostic process are described in detail in the maintenance manual, and will not be introduced here). No problem was found through the test But the focus is still on the ABS controller. Do you want to replace the expensive ABS control unit? When checking the brake fluid again, I found that the clean brake fluid just replaced was a little black again. Recall the whole maintenance process. When replacing the master cylinder and brake fluid, the brake fluid in the brake system was replaced by the conventional exhaust method, but the normally closed valve in the ABS hydraulic controller was closed under the power-off state, and the brake fluid in the second circuit could not be discharged during the conventional exhaust. During the diagnosis of the actuator, the normally closed valve is opened, and the dirty brake fluid in the second circuit enters the whole brake system, making the newly replaced brake fluid polluted and blackened. Next, we can't ignore the basic setting function of v.a.g1522 for the increasing import volume of high-end products Fill and exhaust the ABS system (the specific steps are also described in detail in the maintenance manual and will not be introduced here). After the brake fluid in the brake system is completely replaced, the fault is completely eliminated and has not appeared again so far

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