Shanghai Passat B5 car is difficult to start for a period of time. Sometimes there will be a failure phenomenon when starter does not respond at all. Many parts have been replaced, but the trouble of starting difficulty still exists. Troubleshooting: (1) analysis of the cause of the failure according to the failure phenomenon. The possible cause of the failure is the malfunction of the starter or the starting power supply (the battery or the failure of the battery or the failure of the starting power line). (2) the troubleshooting method has been understood from the related situation introduced by the owner that the starter has been replaced many times, so the focus of the fault inspection is placed on the starting power supply. The voltage between the positive and negative electrode of the battery is 11. 8V, which is basically normal. It is normal to connect the ignition switch and measure the voltage between the junction column of the starter's electromagnetic switch and the negative pole of the battery. It is also normal that the control line of the starter has no problem. If the starter has no problem, the battery voltage is also basically normal, and the voltage is added to the starter, what is the cause that makes the start of the starter low or not rotated? Only the main contact of the electric magnetic switch of the battery positive pole, the motor of the starter, the engine cylinder, the engine of the engine, the frame and the negative pole of the battery have been broken down. Check the connection between the battery pole and the wire clip, the connection of the connection column of the starter power supply and the iron wire of the battery negative pole and the frame. A rough wire is connected to the engine cylinder body and the negative pole of the battery. The engine can start smoothly, so the tie line connecting the engine block and the frame has no doubt. Check the engine's tie line and find that its joint has been oxidized and almost broken. (3) troubleshooting measures remove the damaged engine tie line, clean up the junction of the tie up and install the new engine tie line, and troubleshooting. Fault analysis: the analysis of the cause of oxidative fracture of the engine's iron wire may be that the end of the wiring terminal is loosened. When starting, the large current can produce voltage drop through this place, and it may produce a jump fire to make it oxidize and eventually lead to the fracture of the copper wire. Due to the thinning of the tie line and the poor contact of the connection, it will cause difficulty in starting, and the starter will not rotate when it is serious. This failure check battery condition adopts the method of measuring the static voltage of the battery. This method is relatively simple, but the reliability is not as good as that of the dynamic voltage test. If the conditions permit, the high rate discharge meter can be used to measure the load state, and it can accurately determine whether the storage battery is sufficient or not.