In the training field, some the Great Wall CC5021XLHDLD02 pickup coaches often have occasional water temperature and have a boiling phenomenon. Troubleshooting: first, check the actuator, remove the water temperature sensor to see whether the fan is able to work, check and confirm that the electronic fan can run, exclude the computer can not receive information and send instructions, the executive can not receive instructions and execute the suspicion. The water temperature readings of ECU detected by the data flow of the computer detector are read, and the temperature of the cooling liquid in the water tank is detected by the digital multimeter. The dynamic water temperature of the two is not consistent, and the temperature of the computer inspecting instrument is 11 degrees lower than the digital multimeter. By analyzing this test result, the preliminary judgment is not the computer connection. The information received is inaccurate, and the processing of information is problematic. The fault points are reduced to water temperature sensors, engine ECU and related conductors. Since the car has changed the engine ECU and water temperature sensor, we will check the supply voltage of the water temperature sensor first. After checking the value of the voltage is normal, the emphasis of the inspection is transferred to the line. It is doubted that there is a bad contact in the line, the related plug on the line on the edge detection, the temperature value of the data flow reported by the computer detector has not changed, and the possibility of the bad contact of the connector is excluded. It is found that the resistance of the water temperature sensor to the engine computer is 6 Omega when the conductance and resistance of the wire is checked, and the value is not changed again and again. At this time, the cause of the accident of the accidental water temperature and the opening is the lead. In order to further verify, the water temperature of two places is detected again through one wire. The temperature value reported by the computer detector is basically the same as the water temperature detected by the digital multimeter. The engine is started, the engine temperature is detected, the occasional water temperature of the engine is high and the failure of the open pot is not reproduced. The highest value of the temperature meter also declined slightly. Subsequently, all vehicles with high water temperature have been checked, and the engine wire harness was replaced according to the warranty rules and the fault was completely eliminated.