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The new modified Benz S350 car equipped with M272 engine. User reflection: the car night vision function is not available. After night driving operation night vision function button, information on "night vision system stop work" is displayed on the instrument. Fault diagnosis: connect the DAS diagnostic instrument to the rapid detection of the vehicle. The test results show that the night vision auxiliary system control module N101 can not communicate. Finding ways to establish communication between the control module becomes the primary task of troubleshooting. In view of this failure phenomenon, the analysis may be caused by the following reasons: the power failure of the night vision auxiliary system control module N101, the night vision auxiliary system control module N101 and the dynamic CAN H (dynamic CAN) distributor X30/28 connection fault. The night vision auxiliary system control module N101 control module itself fault 221 night vision auxiliary system A simple diagram of the line control, as shown in Figure 1. First, the power supply of the night vision auxiliary system control module N101 is detected. The circuit diagram shows that the power supply of the night vision auxiliary system control module N101 is supplied by the former SAM control module N10/1 through the F62 fuse. After testing, when the ignition switch is "15 ON", there is no voltage on the fuse F62. The power supply of F62 fuse is supplied by the chassis 87 relay KE on the front SAM fuse and relay module N10/1. After further testing, it is found that there is contact fault in the "KE relay", which is replaced first. After the relay KE is replaced, the vehicle is quickly detected. The test results show that the night vision auxiliary system control module can be communicated, but the night vision function is still unusable. The incoming night vision auxiliary system control module reads the current fault code "5058" storage, which means "the night vision auxiliary system control module N101 and the camera B84/2 connection fault". The night vision switch is operated, and the "night vision auxiliary system does not have this function" prompt information on the meter. According to the analysis of the content of the fault code, there are several possible reasons: the line fault between the camera B84/2 and the night vision auxiliary system control module N101, the internal fault of the camera B84/2 and the internal fault of the night vision assistant system control module N101. Then we observed the data flow as follows: "further actual. values" column, and observed that the component identification number of the B84/2 camera could not be displayed; the "thermal actual values" column was observed to find that the letter number of the B84/2 camera was unavailable. The LVDS line connection between the camera and night vision auxiliary system control module is disconnected, and there is no short circuit and open circuit phenomenon on both sides of the LVDS line. It is a bit puzzled to find the fault. Is it the failure of the control module or the failure of the control module itself? Calmly, the LVDS line between the camera and the night vision auxiliary system control module is normal and does not prove that the two components are in good connection, which is usually easily ignored. The internal connection state of the two components is measured, and the plug of the night vision auxiliary system is pulled down and the short circuit between the pins of the LVDS pins is measured in the condition of the connection of the camera line. The result has finally found the crux, the short circuit between the pin 5 and the pin 10. Pull out the camera side plug measurement and confirm the internal short circuit of the camera. The dismantling camera revealed that its internal wiring board had been seriously corroded and had to be replaced. After enquiry, the customer knew that the car had been flooded. The camera is changed, and the camera is initialized and calibrated by DAS guiding test function. After the calibration is successful, the night vision function of the vehicle is normal. Fault summary: in the process of vehicle fault diagnosis, people have gone through a misunderstanding, write it to share with you. Both infrared light lamps are also part of the night vision auxiliary system. At first, it is believed that the working state of the infrared light lamp plays a decisive role in the work of the night vision auxiliary system. During the detection, it was found that the night vision switch read from the UCP control module operated normally, while the infrared headlamp was always "OFF". The working state of infrared headlights can not be observed directly with the naked eye. The actual value of the night vision switch from the central gateway from the N10/1 is always "inactive", and the Coding of the central gateway on the Xenon headlamp is "inactive". Later, by comparing and testing other vehicles, it was found that the infrared light bulb did not play a decisive role in the work of the night vision auxiliary system. It would only affect the clarity of the work of the night vision auxiliary system. It can also be said that even if the infrared headlights are removed, the night vision auxiliary system can still work. The essence of the initial diagnosis is wrong.