A 2010 Mercedes Benz E300 car equipped with M272 engine. User response: the function of the vehicle parking positioning system is invalid. After the vehicle starts, the R block is hung, the front and rear radar displays are not displayed, the front and rear display buzzer is not screaming, and the reversing lamp works normally. Fault diagnosis: the connecting DAS diagnostic instrument uses Xentry diagnostic program to detect the vehicle quickly. The test results show that the PTS system has the fault information storage: D12B00, and the communication fault with the warning display of the front car positioning system. Enter the fault code, click "test" into the boot test menu, the system will lead the connection between the test PTS control module and the front PTS warning device, and will guide the detection of the power supply of the front PTS warning device. After testing, the power supply terminal of the front warning display is not voltage input when the reverse switch is connected. Dismantling the line between the PTS control module and the COMAND control module under the right front pits, it is found that the wires on both sides are not guided, and the line color of the display is not the same as that of the circuit diagram. Will the line be wrong? The initial check list of the rebrowsing of the vehicle found that, in addition to the current fault code of the PTS control module, the AAC air conditioning control module also has the current fault information with the communication fault of the internal temperature sensor. It can be assumed that the plugs of the two components are the same, and the line inserting is reversed. With the attitude of trying to see, checking and checking the two component control lines, it confirms that the hypothetical situation is a real problem. No wonder, because the car has just been transferred from the second-hand car market. This kind of failure is virtually zero in actual maintenance. After the line is reset, PTS and air conditioning function return to normal. For the maintenance of the PTS system, there are several experiences for reference: if there is a component fault (such as radar sensor, warning display), the whole system will stop working. The installation position of the front plate frame is improper or the license plate frame is not installed, which will lead to the PTS system misalarm and PTS system working conditions. At the same time, with the hand touch or the ear close to the radar probe, the vehicle can feel or hear the fluctuation. For the vehicle with special functions such as the equipment stationed in the car or the blind spot monitoring function, the radar probes in the middle and the two sides of the bumper are different and can not be mixed. The order is based on the EPC number.