Symptom: When driving the front left of the vehicle abnormal sound.
    Fault diagnosis: This car was originally due to automatic transmission failure into the factory maintenance, road test to hear the left front of the vehicle has a sound, the sound came from the brake cylinder. But at this time the driver did not step on the brake pedal. Began to suspect that the brake cylinder is caused by the card. The vehicle lift up with a lift, start the engine, hand the left front wheel can be free to turn, but go to a certain speed. The wheel is automatically locked. Obviously the ABS system works. Control brake cylinder action brake wheel. In order to confirm the ABS system or mechanical problems, the ABS control unit plug unplugged again. The fault no longer occurs. At this point you can determine the problem lies in the ABS system. With the diagnostic instrument into the ABS system, no fault code; into the data flow to observe the four wheel speed sensor signal, the diagnostic instrument shows the wheel wheel speed signal is basically the same. Also normal.
    In the absence of step on the brake pedal. ABS system action brake wheel. The problem should be out of the wheel speed sensor, but the diagnostic test is normal, is the control unit is broken? This car into the factory is to repair the automatic transmission, the need for a long time to test, decided to exclude automatic transmission failure. The next day to continue road test, the vehicle driving a few minutes later. ABS fault warning light suddenly lit, the fault light when the left front wheel no longer abnormal sound. Read fault code 00283 (left front wheel speed sensor defect) with a diagnostic instrument. The same trouble code appears after clearing. Remove the wheel speed sensor and found that the sensor head has been flattened by the ring gear. Remove the right front wheel speed sensor check. The sensor's head is also polished. Desperation, holding the psychological try, in the two wheel speed sensor on each plus a gasket after the back. When the test is no longer abnormal front wheel, ABS work is also normal, the fault actually excluded.
    Fault Summary: As mentioned earlier. This car is for the maintenance of automatic transmission from the left front wheel noise is in the road test automatic transmission shift process is generated in the maintenance process there are many theoretical difficult to explain the place, the following we discuss these doubts.
    1. From the vehicle into the factory when the ABS system is normal, to fault but the fault warning light does not shine. The final fault warning light light memory 00283 (left front wheel speed sensor bad) fault code, indicating that the wheel speed sensor head is gradually worn off by the ring gear. But why is the wheel speed sensor head worn out? Some people think that the installation is not properly caused by the gap between the sensor and the ring gear is too small. But people who have disassembled the wheel speed sensor of this car will know. The sensor is directly inserted into the mounting hole, the gap can not be adjusted. Some people say that because the wheel speed sensor is too long (not the original) and grinding to. After checking a sensor and asking the owner, the sensor is original. The final opinion is more uniform is the bearing loose caused by ring gear and grinding to the head. But the two front wheels are so ah. Both sides of the bearing at the same time loose probability is too small! Because the car had recently occurred in traffic accidents. So that this and the front of the vehicle was affected by the impact.
    2. Since both sides of the wheel speed sensor head are worn away. Why the fault only appears in the left front wheel, the fault code only the left front wheel 7 in fact the right side wear more powerful than the left. I think. The left side of the wear is not serious, the resulting signal on the control unit but not normal. That the left front wheel speed too fast. So the pressure on the left front wheel (rather than release the pressure.) Control the left front wheel cylinder brake caused by abnormal sound.
    3. When the fault first appears when the fault light does not light, with the diagnostic test and no ABS system fault code (later fault lights. ABS does not work when the failure does not appear). But the diagnostic instrument shows the four wheel speed sensor signal is normal, ABS control unit in the driver did not step on the brake when to brake the left front wheel 7 final proof. ABS control unit no problem. Had to force the responsibility to the diagnostic instrument - the data flow is not accurate.