The Volkswagen Santana 2000GSi limousine with a mileage of about 150 thousand km. The ABS indicator lights on the car, and all wheels are locked when emergency braking. Fault diagnosis: first, the fault code is transferred. Jinde K81 multifunctional diagnostic instrument is connected to the diagnostic socket under the shift lever sheath, the ignition switch is opened, the operation diagnostic instrument enters the anti lock brake system, and the function of "reading fault code" is selected. After pressing the confirmation key, the diagnostic screen shows "01276 one hydraulic pump V64 signal exceeds the tolerance". After the fault code is selected, the function of "clearing fault code" is selected, and it is found that the fault code can not be cleared. Select the "control component test" function. It is also found that the function can not be executed, that is, to select the "control element test" function. After pressing the confirmation key, the diagnostic screen displays "test end", the ABS indicator does not flicker, and the sound of the hydraulic pump work is not heard, so it is the same for several times. The fault is analyzed according to the hint of the fault code. If the ABS hydraulic pump is damaged simply, it should be able to test the control element with the diagnostic instrument, that is, the diagnostic instrument and the indicator should change. Will it be that the circuit is in bad contact? Referring to the circuit diagram, the 29 fuse located at the top of the central relay box is called the hydraulic pump fuse (30A). When the ignition switch is turned off, it is checked that the fuse is in good condition. Then the fuse (30), ABS solenoid valve (30A), was inspected, and there was no fusing phenomenon. To determine whether the connection is good, swap the 2 fuses and turn on the ignition switch. The ABS indicator on the dashboard is lit for about 3S and then extinguished. Try to remove the fault code with the instrument and perform the "control element test" function, the fault code can be cleared, the ABS indicator flickers continuously when the test is executed, and the sound of the hydraulic pump can be heard, indicating that the control system is normal. Check the connection line of the battery (the power supply of the ABS hydraulic pump and the solenoid valve are supplied by the battery directly). It is found that the battery negative connection is loosened because of the damage of the card. The battery is retightened and the ABS system is restored to normal.