Swing the steering wheel is something that everyone has to do every day, but one day suddenly the instrument steering wheel fault light is on, and the instrument and display screen also prompt "active steering system failure!"! When turning, please pay attention. "Do you panic? Don't panic. I hope the following dry goods can bring you peace of mind.
First understand BMW's active steering system
BMW active steering system mainly consists of steering gear, power steering pump (integrated hydraulic pump), electric control valve, hydraulic oil storage tank, hydraulic oil cooler and some actuator components. It is similar to the traditional steering system in appearance, except that a double planetary gear mechanism is added between the gear and rack of the traditional steering system to provide the superimposed steering angle for the front wheels.
In other words, the active steering system uses overlapping steering gear, which is mainly composed of planetary gear mechanism, turbine, worm drive mechanism, servo motor, servo motor position sensor, electromagnetic lock, etc. The active steering system controls the servo motor according to the speed, steering angle and other signals. The servo motor is fixedly connected with the worm drive mechanism and embedded in the turbine in a gapless way, so that the planetary gear components can be driven, and the purpose of adjusting the steering angle and changing the steering transmission ratio can be realized. The direction, speed and duration of motor rotation are monitored by servo motor position sensor to calculate redundant steering angle.
In active steering system, the steering gear has variable transmission ratio, that is to say, the corresponding relationship between steering wheel angle and wheel angle is variable. Then, the active steering system can actively increase or decrease the steering angle of the front wheels when the driver turns the steering wheel according to the specific driving conditions. Generally speaking, when the vehicle is stationary or at low speed, the driver only needs a small range to turn the steering wheel to achieve a larger steering angle of the front wheel; while at high speed, the driver needs a large range to turn the steering wheel to achieve a smaller steering angle of the front wheel, thus eliminating the high-speed steering drift. In this way, regardless of high speed and low speed, the driver can get a good steering feel.
Let's talk about the cause of active steering system failure
1. There are several common reasons:
a. Steering angle sensor failure;
b. Servo motor position sensor fault;
If there is a fault code related to the steering angle sensor or servo motor position sensor when it is taken for diagnosis, the fault point is estimated not to run. Generally, it can be solved by checking the relevant sensor and its related harness. It should be noted that the position sensor of servo motor cannot be replaced separately in 4S shop, so if it is out of warranty, you can try to repair the chip.
c. Steering column module failure
The reason why there is no speech here is that the steering column switch center (SZL) is too dirty, which causes the corner signal to be too weak, the computer can't detect or the detected signal is not credible, so the fault is reported, we can clean it up, especially the corner sensor. To be honest, dismantling and cleaning are laborious and do not make money. It depends on your luck whether you want to change or clean it up, but it's usually bad luck.
Here's a brief introduction to the fault principle: the corner signal is generated by the light-emitting diode passing through the lens and grating to the receiving diode. If the lens becomes dirty, the light will be lost in the process of propagation, and the signal will naturally become weak.
d. Wheel speed sensor failure
If the instrument still has the fault lamp of DSC, the wheel speed sensor and its circuit can also be focused on.
2. Communication problems lead to active steering system failure
Active steering system generally receives signals and data from various sensors and control modules through f-can bus, and then transmits data with engine computer, safety and gateway module through pt-can. If communication problems are detected, the bus can be checked first.
3. Aging and leakage of steering harness
If there is no obvious fault code to diagnose, and it can't match the steering machine, if you suspect that the steering machine is ready to be replaced, you may as well check the wiring harness of the steering machine, which may save money.
4. Storage capacity of battery is insufficient
If you often report that the active steering fails when you start a cold car, and the steering wheel is heavy, but after a period of driving, everything is normal, then it can be doubted that the battery is not working. It needs to be replaced.