Symptom: a Nissan style 3.0 car driving step on the first foot brake pedal found that the beginning also felt under the soles of the feet are very strong, can be stepped on the normal step on the fixed position, it seems like suction, brake pedal Down in the end.
    Troubleshooting: first suspected to be a vacuum power problem, can be a careful analysis, that has nothing to do with the vacuum power. Check the vacuum booster again, it really no problem. Before taking over the car, other colleagues have changed the three master cylinder, did not solve the problem. In the brake system connected to the oil pressure gauge and found the first foot brake, the left front wheel oil pressure can not be established, the oil pressure reaches 7-8MPa, immediately fell to 2-3MPa; the second foot can reach 12MPa; Two rounds of oil pressure are no problem, you can go to 7MPa or so. The car on the brake force detection station, the braking force detection no problem. When using a dedicated computer on the ABS system test found that the left front wheel and right rear wheel can not pressure (only a small part of the leakage), and the normal can be depressurized to very low. For example, the normal front wheel braking force to 20MPa, can be pressure to 3-5MPa. Rear wheel braking force to 15MPa, the pressure can be reduced to 3-5MPa, ABS pump seems to have problems.
    After replacing the ABS pump, the problem is solved. After understanding the car had hit, it may be accidentally hit ABS pump internal split, resulting in pressure relief.