A car mileage of about 110 thousand km, the model is E70, equipped with N62 engine in 2010 BMW X5 SUV. Users reflect: when the vehicle runs on rainy days, the steering system fault lights sometimes light up. Inspection and analysis: maintenance personnel detect steering system control unit, store fault code "613A - active steering control system power supply voltage is too low". After the fault code is removed, the driving mode is tested and the fault lamp of the steering system is lighted again. The fault code is still unchanged. Check the active steering control unit in the front row passenger foot space and find that the power line is 6 mm2 wire, because the output power of the steering motor is larger. It was found that the fixed bolt of the tie - in point X165 was loosened. The analysis holds that, when the vehicle runs on a rainy day, the driving posture needs to be regularly adjusted because of the slippery slippery road. In this case, the active steering motor will run frequently, which will make the X165 iron lap hot and cause the increase of contact resistance. Troubleshooting: tighten the X165 tie point bolts, test again, and the fault lights no longer light up, confirm troubleshooting.