Dongfeng EQ1090 truck is difficult to start because of low starting speed, and the driver considers it to be a battery failure. The battery is recharged and recharged by constant pressure. The battery charges 12h, and the charging process is normal. After the battery is loaded, the starter is still unable to start, and the engine is hard to start. Troubleshooting: (1) the possibility of failure analysis from the failure phenomenon analysis of the possible causes of the battery loss electricity, battery plate vulcanization, the starting circuit connection bad contact, the starter has trouble and so on. Because the battery has just been charged and the charging process is not abnormal, the possibility of battery loss and plate vulcanization is preliminarily eliminated; the battery cable is just connected and the connection column connection of the starter power supply is very strong, so the possibility of the failure is only the starter. (2) the fault diagnosis method takes the starter off and uses the battery as the power supply to carry out the no-load test and the full braking test to test the starter's performance. The test result shows that the starter has good performance, and the starter is still unable to run after re loading. Touch the wire clip on the pole of the battery and feel the heat. After the clamp is removed, the inner surface of the battery is found to be dirty (copper rust). The failure of the inability to operate the starting machine is caused by the bad contact. (3) troubleshooting measures rinse the clamp with clean water and then tighten the cable clamp again. Fault analysis: generally, the most likely failure of the starter to operate is the loss of battery power, and the second is the bad contact of the connection of the starting power line. However, the battery has just been supplemented and the charging process is normal, so the possibility of battery loss and plate vulcanization is eliminated. The connection between the pole and the clamp of the battery is just connected, and it is very strong. Therefore, it is mistaken that the connection of the starting power supply line is no problem, and the troubleshooting has taken a detour. The example of the fault maintenance provides two points of inspiration: when connecting the cable clip on the battery pole, we should pay attention to check the dirt, oxidation and rust in the wire clip. When the starting speed is too low, do not only judge whether the connection is good or not according to the strong connection of the starting power line, but also through the multimeter. The voltage drop (starting time) or contact resistance (circuit breakage) is used to check whether the connection is bad. If there is no multimeter, you can use hand to feel the temperature of the circuit connection to determine whether the joint is in good contact. When contact is bad (contact resistance), large starting current will generate heat when passing through.