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A Volkswagen ten meter car with a mileage of about 80 thousand km and equipped with a 1.8TSI engine in 2009. User reflection: when the car runs to the intersection with red light, it uses the parking brake. When the electronic parking brake switch is released, the vehicle is found to light on the electronic parking brake fault indicator light on the dashboard, flicker the vehicle indicator light, the electronic parking brake switch indicator light flickers and the right rear wheel electronic parking brake is not released. Put it. There was a similar failure before the car. After the fault code was removed from the distributor, it only ran for about 400 km, and the fault happened again. Inspection analysis: after taking the car, the author first uses the public special diagnostic instrument VAS5051 to read 3 fault codes in the electronic parking brake system, which are 03200---- electronic parking brake button switch E538 fault, 02435 - power supply voltage circuit breaker / short circuit on the right channel of control unit and 02442 - operation unit function light circuit breaker / Short circuiting by accident. According to the structure of the fault code and the electronic parking brake system, the reasons for this fault include the failure of the right rear wheel electronic parking brake motor (V283), the electronic parking brake control unit (J540) fault, the J540 power supply and the bypass fault, the J540 right and V283 line break or short circuit between the right and V283. According to the circuit diagram, the resistance of V283 two terminal T2ao/1 and T2ao/2 is measured about 0.52 Omega, and the 12V voltage is applied to both ends of V283. The motor can operate normally, indicating that the V283 work is normal. The wire resistance between T30/12 and T2ao/1, T30/27 and T2ao/2 is respectively measured to be 0.05 ohms, indicating that the connection line between J540 and V283 is normal. When pressing the electronic parking brake switch, the voltage between T30/12 and T30127 terminals of J540 is 0V. Obviously, this is not normal. Check fuse SD2, SC29 and SC30, and do not fuse. The voltages between T30/13, T30/15 and T30/22 terminals of J540 were 12.5 V, respectively. The resistance of conductors between SD2 and T30/22, SC29 and T30/13, and between SC30 and T30/15 is respectively measured to be 0.05 ohms, indicating that the power supply line is normal. The resistance between the T30/28 and T30/30 terminals of J540 and the body of the body is re measured, which is 0.05 ohms, indicating that the J540 is normal. At this point, the author suspected that J540 was defective, so the J540 test was replaced and the fault phenomenon was eliminated. But the original car J540 installed to other vehicles test, electronic parking brake work is normal; so the original car J540 back, the failure phenomenon also disappeared, thus the original car J540 and no failure. At the time of diagnosis, though the fault was eliminated, the real cause of the failure was not found. The vibration method is used to simulate the fault symptom, and to connect the connecting wire and the connector which are related to the electronic parking brake of the right rear wheel. When shaking the fuse SC29, it is found that there is obvious signs of loosening. After pulling out the fuse insert, it is found that one of the sockets is cracked on both sides. Troubleshooting: Troubleshooting after using the special tool VAS 1978 to reprocess the SC29 fuse socket. Review and summary: for the accidental fault of the electrical system, through the general inspection can not find the cause of the fault, the fault symptom simulation test can be carried out to try to reappear the fault. This example is to use the vibration method to simulate the poor contact situation of the power supply line, and finally find the fault point. For the examination of fuse, we need to check whether the fuse is in good contact with the socket and whether the fuse is in good contact with the fuse. This is due to the neglect of the good contact between the fuse inserts and the pins during the examination of the fuse, which brings some unnecessary work.