The BMW 3 Series car was not a trailer to enter the factory. The car was first to be repaired by my colleagues. I didn't know much about the situation when I entered the factory. Then I took over the car because of other things from my colleagues. First, explain the fault phenomenon: the ignition switch can not be opened to the two ends, the central information display, air conditioning and so on can not work normally. Matrix diagnosis: because the vehicle can not open the ignition switch, so ICOM can not enter the vehicle, the diagnosis system can not be diagnosed, the maintenance lack of the right hand, can only rely on their own groping. First of all, I wonder if the battery is dead. Try to click the horn and find the loudspeaker loud, which indicates that there is no loss of electricity in the battery. For a moment, I can only use one of the most stupid methods, inquire about the power supply of the vehicle, measure the fuse on the fuse, find that all the fuse of the KL.15 control has no electricity, and the KL.30B fuse has the vehicle voltage, indicating that the KL.30B can be connected. It is doubted that the remote key signal transmission is not good or interfered. According to the emergency start step, the key near the emergency boot antenna of the steering column is tried to start and still cannot be started. In many attempts, it was found that the display area of the vehicle displayed a string of English, probably meaning that the remote key could not be activated. With this hint of English prompt, we begin to explore the only clues. Since the rear shades can not be lowered, there is no way to measure the key signal near the antenna amplifier, check the fuse F104 of the antenna amplifier and check the existence of the vehicle voltage on the fuse, which can not be measured. Next, the transmission signal is measured on the corresponding PIN5 of the FEM (front electronic module). It is found that the voltage will jump between 10.8 and 11.1V without the remote control, and the key pressed by the remote control will be reduced to 10.4V. If hold down for a long time, it will be reduced to below 10V. Check the plug of FEM and PIN foot is normal. Combining the circuit diagram, it is not difficult to see that the signal line of the antenna amplifier to the front part of the electronic module is the LIN bus. Because of the problem of the oscilloscope, the voltage is measured by the multimeter. By contrast, it is found that the voltage is credible. It is preliminarily determined that the antenna amplifier can recognize the remote key key operation and transmit the signal to the FEW. Is there a problem with the key launch signal or is the FEM receiving the signal not processed further? In order to determine which place exists, the key is read on KEY-READER of the reception department and the chassis number is consistent with the vehicle. The possibility of the abnormality of the key is preliminarily excluded. Finally, the doubt fell on FEM and KL.15 relay. The car has two fuse boxes, through inquiry data found that two fuse have KL.15 relay, experience shows that two relays at the same time the possibility of damage is very small, the measurement of the FEM KL.15 control foot repeatedly press the button, the voltage has not changed. In order to further confirm that the two fuse boxes of other cars are still switched off, the FEM damage is determined. In order to eliminate damage caused by software, reprogramming the vehicle has not improved. The price from ten FEM is very expensive, so for careful sake, we will check again. Since the previous diagnosis of EPS (electronic steering machine) did not communicate with the fault code, check the EPS power supply, iron lap normal, check KL. 15 to EPS power supply voltage does not exist, check the EPS bus voltage normal. Check the power supply of FEM and REM (rear electronic module) normally. The final confirmation of the need to replace FEM. After ordering for half a month, FEM will be installed, and the failure of programming trial will disappear. Troubleshooting: update FEM and program and code the vehicle. Fault summary: in our daily repair work, when we have ideas, we must verify, we can not rely solely on experience to judge. In addition, through the maintenance of this car, we can also use another method for similar failures: a wire is used to diagnose OBD II's PIN1 and PIN16. This is the way I have just learned, and I would like to share with you here. Background knowledge: F30 also uses the front electronic module FEM. FEM takes the place of the following control units: the junction box (JB), the convenient boarding and starting system (CAS), the comfortable boarding system (CA). The foot space module (FRM) ZGM is integrated in FEM as an independent control unit, and FEM is located on the A column on the front passenger side. In FEM, it provides protection for the following function through the fuse: the steering column switch center (SZL), the driver auxiliary system operation unit, the light operation unit, the driver LED front light module, the rear electronic module (REM).OBD II plug, the IHKA. car door lateral pull electronic device, the electric window elevator, the control lock below. The function is connected through the relay in FEM: the driver side electric car window elevator, the front passenger side electric car window elevator, the middle lock, the headlight cleaning device, the boot machine, the horn. The wiper block position 1/2.