A 1999 BMW 750iL (E38) complaint shock absorber hard. Test, car shock is very powerful, like no vibration. But the instrument and switch indicator function is normal. Ask the owner how the failure occurred, the owner told the steering wheel and made a four-wheel positioning after the hard. Use GT1 to detect no fault record, see the data stream, find the steering angle + 25 °, not normal (wheel and steering wheel in a straight line position). Other data is normal, it is estimated that the failure occurred in the steering angle. Use the GT1 to adjust the steering angle sensor to zero (the current steering wheel position as the steering wheel of the linear travel position is permanently stored in the steering angle sensor EEPROM. Therefore, the adjustment of the front wheel and steering wheel must be accurate In addition, the chassis model in the instrument panel is permanently stored in the EEPROM of the steering angle sensor. The fault stored in the steering angle sensor will be automatically deleted after the successful adjustment). everything is normal!
    We analyze from the principle why the steering angle in the straight line position is not zero will affect the shock absorber hard.
    Electronic vibration control system Ⅲ (EDC Ⅲ) is an electronic damping force adjustment system. The system adjusts the damping force of the shock absorber to match the current driving conditions and road conditions to ensure maximum driving safety and comfort.
    As part of the chassis, EDC III's task is to compensate for the dynamic forces acting on the vehicle during travel. The following forces will act on the vehicle:
    The vertical force, for example, is caused by uneven pavement
    Lateral force, centrifugal force crosswind / turn
    Longitudinal force, acceleration / braking
    The task of the chassis is to receive the force transmitted to the vehicle. And most of this task can be completed by the shock absorber, EDC Ⅲ's main task is to maintain a high driving safety while improving driving comfort. For this reason the system is equipped with the following sensors for sensing driving conditions: steering angle sensor, speed sensor, front body acceleration sensor, rear body acceleration sensor. According to the travel status data of these sensors. The damping valve integrated in the damper is adjusted to the soft, medium or hard corresponding gear by the EDC III control module.
    The driver can select two different programs via the EDC III program button: the button S position represents the motion mode program, and the button K position represents the comfort mode program. Motion mode The shock absorber is hardened. That is to avoid the shock absorber soft. At position K, the 3rd block works at the same time. There is a motion mode characteristic line and a comfortable mode characteristic line.
    When using the button to select the EDC III program (motion mode and comfort mode). An LED that is integrated in the button can show which program is being selected. If the LED with the symbol S lights up, EDC III works in the motion mode program state: the LED does not light, then work in the comfortable mode program state, of course, this applies only to the normal operation of the EDC Ⅲ system.
    If the EDC III system fails (for example, sensor damage) or a certain degree of failure, then it can not guarantee the safety of the vehicle in any way, so a safety model integrated in the EDC Ⅲ control module software will shut down the entire EDC Ⅲ system. In this case, the LED on the select button is extinguished, the same as when the motion mode program is turned on. In the case of system power failure in order to make the vehicle can continue to travel safely, the damping valve to switch to power, that is, running in hard mode. Although the vehicle is in a very hard state of vibration, but no loss of adhesion can also find the nearest repair station.
    1. Steering angle sensor
    The steering angle sensor (shown in Figure 2) has two potentiometers that are offset from each other by 90 °. The steering wheel angle measured by the potentiometer is the whole rotation of the steering wheel. That is, every ± 180 ° angle value will be repeated. The steering angle sensor identifies this and calculates the number of turns of the steering wheel. therefore. The total turning angle of the steering wheel is calculated from the currently measured steering wheel angle and the number of revolutions of the steering wheel.
    In order for the total turning angle of the steering wheel to be readily available, all steering movements must be measured without interruption, including when the vehicle is in a stationary state. To achieve this. The steering angle sensor is continuously powered by a constant current (battery voltage). So that even when the ignition switch is off. Steering motion can still be measured. The steering angle measured by the potentiometer after the ignition switch is off is still available, but the number of revolutions of the steering wheel is not recorded.
    In order for the steering angle sensor to remain functional after power failure. The sensor incorporates a software that calculates the number of turns of the steering wheel by means of the wheel speed (in addition to the wheel speed on some models, also by adjusting the steering wheel from one extreme position to another). This process is called the cycle count calculation process. The steering angle sensor is fault-free in both cases.