Troubleshooting of braking system caused by dirty

2022-08-08
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Troubleshooting of brake system caused by dirty brake fluid (II)

fault summary:

the car is caused by Because the brake fluid is too dirty, it is not replaced in time, and the impurities in the brake fluid accumulate on the normally closed valve, resulting in the sealing failure of the normally closed valve sometimes?? Analysis and research, but simply replace the ABS control unit The fault is naturally eliminated, but it is bound to bring unnecessary economic losses to the owner

another similar example: the age Superman fault is that during driving, when pressing the brake pedal in an emergency, there is a sense of the end of one foot, which is very active Longer braking distance only occasionally occurs Sometimes once a day, sometimes once a few days

check the front and rear brake friction plates The brake disc and drum are worn normally, the front and rear brake wheel cylinders and the pipeline connections are normal without leakage, the brake master cylinder liquid level is also normal, but the brake fluid color is black. Due to the maintenance experience of the above example, the basic setting function of V.A.G1552 is used to completely replace the brake fluid, and then the fault no longer occurs

case 2

fault phenomenon: a 1998 Santana 2000GSi car Press the brake pedal and feel the height is normal When stepping on the brake pedal during driving, I feel that the braking is not sensitive, the braking distance becomes longer, the performance decreases, and the ABS fault light sometimes flashes

fault diagnosis:

first of all, in view of the fact that the ABS fault light of the vehicle sometimes flashes, the equipment is suitable for the test of dynamic and static friction coefficient when plastic film, sheet, paper and other materials slide. When it is on, connect the fault diagnosis instrument V.A.G1552 to enter the ABS system and query the fault code. It was found that there was an accidental fault record of the speed sensor of the right rear wheel. After clearing the fault code, the test run was carried out, and the data flow was read. It was found that the speed of the right rear wheel was basically the same as that of the other three wheels, and the fault light had not been lit during the test run. Looking back, I checked the brake fluid and the front and rear brake pads, brake discs, and brake drums. I found that the brake pads, discs, and drums were worn normally, and the brake fluid was dirty. At the same time, I also found that when the right rear wheel stepped on the brake pedal, the right rear wheel could rotate with hand force. Directly loosen the bleed screw of the right rear wheel cylinder. When the brake is pressed, no brake fluid flows out. After Remove the oil pipe connector of the right rear wheel cylinder from the ABS control unit, and there is still no brake fluid flowing out when pressing the brake. When the oil inlet pipe on the ABS control unit is removed, brake fluid ejects, which is particularly dirty and thick. The owner of the car was asked that he had never changed the brake fluid after driving 120000km, and he didn't know that the brake fluid had to be changed. So far, the cause of the fault is clear, that is, the pipe or normally open valve in the ABS control unit is blocked. At this time, is it disassembly or replacement of ABS control unit? Is there a way to neither disassemble nor replace the ABS control unit? Only one try! That is, when the air release screw of the rear wheel cylinder is loosened Use the basic setting of v.a.g1522 and the diagnostic function of actuator to operate repeatedly. When the original control mode of the whole system for the fifth time was to diagnose the components before the tension reached the set tension, suddenly a black and dirty brake fluid was ejected from the right rear wheel cylinder. Then, use the basic setting function After the brake fluid is completely replaced, the braking becomes sensitive The ABS fault light no longer flashes

another similar example: a 1995 Passat B4, due to poor braking, replaced the four-wheel brake pads elsewhere. After the operation, it successively assumed the titles of heads of more than 10 teams, such as security, military reform, finance and economics. During the process, it removed two rear wheel cylinders from the vehicle. After replacing the brake pads, when bleeding the rear wheel cylinders, it was found that there was no air and brake fluid flowing out of the two rear wheel brake cylinders at all. So he came to me to ask for help. I checked and confirmed that the problem was solved by adopting the same method as the above example due to the internal blockage of the ABS control unit. In daily actual maintenance operations, flexible use of each function of the equipment and finding some tips can not only reduce a certain amount of work for yourself, but also save money for car owners_ Some unnecessary economic losses

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