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There are 2013 BMW 730Li cars with mileage of about 4000km. Users reflect: after the vehicle is suspended again, the EMF yellow fault alarm lamp in the instrument is on the alarm. The monitor shows the failure of the parking brake, and the vehicle can run normally. Fault diagnosis: after receiving the car, first through ISID diagnosis and detection, read the following: 480AOD -DSC: EMF, fault, speed signal, 480526 a car brake button: functional lighting power supply here EMF is an electric mechanical parking brake, the driver can pull the parking brake button to enable EMF Parking brake function. The parking brake is used as a parking brake. The parking brake is operated by the parking brake button in the central console. The parking brake is used to ensure that the stationary vehicle does not move on its own. When the engine is shut down, the EMF bears the parking function, and the servo unit is driven by electric machinery. During engine operation, dynamic stability control (DSC) takes on parking function and is hydraulically controlled through 4 wheel brakes. Identify the driver's absence (safety belt contacts and door contacts) and tighten them in a tear thief way. The servo unit is fixed on the rear bridge beam. The servo unit of the parking brake has been waterproof and sealed. The shell can not be opened in the service of after-sale service. The servo unit is composed of the following components: EMF control module, electric motor, transmission and force sensor, and some electrical appliances are supplied by EMF (2 bus ends KL.30). The cable can be adjusted by electric machinery through the transmission mechanism connected by the electric motor and the flange. At the same time, the pulling wires are respectively applied to an expansion lock with a locking drum wheel brake. The force sensor provides the adjusting force signal to the EMF control module. Recording the adjustment force is necessary to ensure the required braking force. A spring is integrated in the force sensor (the cable terminates therein). The force sensor performs a primary displacement measurement when the spring is pressed. The displacement measurement is based on the Holzer effect. The parking brake button is located in the central console, after the selection button (GWS). The parking brake button is simulated in the logic of hand brake summer A: pull up the parking brake button: the parking brake activates and presses down the parking brake button: the parking brake is in the engine running, the dynamic stability control (DSC) takes on the parking function and passes through 4 wheel brakes in hydraulic mode. Identify the driver's absence (safety belt contacts and door contacts) by mechanical means. In addition, DSC will also send the speed of the buried wheel to EMF in the form of frequency modulation signal (measured by the rear wheel speed). The signal is transmitted on a single wire. This signal is particularly important for the ten vehicle to identify the rest of the vehicle. The ICM control module sends driving speed to EMF. The speed of the transmission of the automatic transmission is also used for reliability checking. There is a functional lighting on the parking brake button, which is illuminated through red LEI to remind the driver parking brake to engage. The EMF control module controls the LED directly. Referring to the technical letter of the manufacturer, we find that there are related cases and solutions. The theme is "yellow EMF warning light and check control information". The production date of vehicles is F02 between June 28, 2013 and October 2, 2013. The fault phenomenon is the check control information and yellow warning that display EMF in the instrument cluster. The fault is caused by the internal design change of the EMF switch, which has no effect on the operation of the vehicle brake system. The fault codes in the EMF and DSC control modules are searched through the diagnostic tests: EMF stores the fault code "480526 - parking brake button: function lighting lamp power supply". DSC stores fault codes "480A0D----DSC: EMF, fault, speed signal". The malfunction of the car, the content of the diagnostic test and the failure phenomenon and diagnostic content of the circular are the same. The production date of the vehicle is also within the scope, so it is identified as a EMF switch failure. After EMF switch is replaced, troubleshooting, deletion of fault storage, trial run, yellow EMF light and check control information are not repeated, troubleshooting.