The Ford Mondeo car, which runs mileage of about 176 thousand km, is 2006. User response: the vehicle can not start after a week's shutdown. Fault diagnosis: first, charge 3H to the battery, start the vehicle after sufficient electricity, measure the generator charging voltage with multimeter, and charge the idle voltage at 13. 5V. Turn on headlights and blowers and other electrical equipment to increase generator load and reduce the charging voltage to 12.4V. Increase engine speed to 1500r/min, generator output voltage up to 13V. Ford's special diagnostic tool WDS is used to enter the PCM to observe the data flow of the generator. No abnormalities are found, so that the generator charging is basically normal. Use the multimeter to detect the parasitic current of the car body, remove the battery negative pole cable, use the multimeter to connect the battery negative pole and the body lift wire, lock the vehicle and decrease the current value to 200mA in 10s. Because the PCM (power control unit) has a delayed standby time of about 20min, this time will maintain the 200mA current basically unchanged. After 20min, the value of the ammeter has dropped to 50mA, indicating that there is a leakage phenomenon in other parts of the vehicle (the normal value should be about 2mA). The leakage current is checked by the method of drawing fuse, and the ammeter is observed. The current drops to 2mA when pulling the fuse. The distribution section of the reading circuit diagram shows that there are small fuse F60, F65, F66, F68, F70, F71, F72, F73, F74 and battery saving relays from the F7 (50A) fuse. Pull the fuse one by one, and when the power saving relay fuse is pulled out, the current value drops to normal. Because the power saving relay is controlled by PCM, the replacement of PCM does not exclude the failure. Windows and doors are controlled by PCM. Will there be problems in doors and windows? Repair door and window circuit, back to the original vehicle PCM, failure or not ruled out. Check the circuit diagram again, check all the small fuse and circuit involved in F7 power supply, fuse F61 and F62 to power the window, F99 power supply to the door side lamp, that is to say, after the F61 and F62 are pulled down, it can judge the circuit in the door, so it can be sure that the control circuit of the battery electric relay is short circuited. It is detected that the circuit has a short circuit due to wear and tear. Handle the wire wear and tear out. Fault summary: (1) in the maintenance of battery loss power failure, first of all, should be confirmed whether human caused, such as whether the owner forgot to close all kinds of lighting, unauthorized installation of various electrical equipment and so on. If there is no problem, the battery charging situation and the leakage of the body electrical appliances will be checked one by one. Inspection of the battery should first observe whether the inspection hole is green, and then use the oscilloscope to detect the waveform and working frequency, which can correctly judge whether the charging situation is normal. The method of connecting the negative electrode of the battery with the body line can not reflect the real situation of the leakage, so the current function must be detected by the diagnostic instrument to read the leakage current. If the current value of the test is within the normal range, the test time should be extended so as to correctly judge the fault and further improve the quality of maintenance. Now the distribution of cars is becoming more and more abundant, many of them are universal, but the loading procedures are different. With the continuous upgrading of automotive technology, the hardware failure rate of vehicle control system will be lower and lower, and the soft failure rate caused by error signals will continue to rise. Fault review: the case of fault and I in the second chapter of this book review of another case, "2.9 rapid leakage fault" similar, the cause of the battery loss of electricity I have discussed in this article, this article no longer praise. I agree with two points of the author's summary of maintenance. The first point is the steps of fault diagnosis. First of all, we should ask the owner: how long does it take to start the vehicle? What time can not start in the day? What is the size of the starter and the brightness of the panel lighting when starting the vehicle? Are there any repairs and electrical appliances in the vehicle recently? What is the mileage of the car? How long is the battery used? Wait. Then test, if the ordinary battery to detect the electrolyte level and the relative density of the electrolyte, if it is the maintenance free battery to observe the color of the inspection hole, and then use the battery tester measurement, and finally measure the charging voltage and working frequency. The second point is the fault diagnosis method. If the leakage current is small, the light bulb will not light at all. If the leakage current is large, the light bulb is lit, but it is only qualitative check. The meter should be checked with the ammeter or the citrus ammeter and the storage tank tester. In the past, the static current of old vehicle batteries was large, mostly caused by faults such as switch contact adhesion, insulation failure caused by electrical appliances or wires. The new car is now equipped with one to dozens of electronic control units, and the static current takes into account the bus sleep power consumption and makes the fault complex. As the author of this paper predicts, the soft fault rate caused by the error signal will rise continuously.