A Chevrolet Cruz car with a mileage of about 100 thousand km in 2010. The user reflects: the car has a high water temperature. Inspection and analysis: maintenance personnel detect engine control unit and find fault code P00B7 - insufficient coolant flow in engine radiator. Refer to the maintenance data, the engine control unit determines the flow according to the temperature difference between the upper and lower radiator of the radiator. When the temperature difference is too large, it indicates that the heat capacity of the coolant flowing through the radiator is too low. Usually this is caused by insufficient flow of coolant in the radiator, when this phenomenon occurs, the heat generated by the engine can not be brought into the radiator for heat exchange. When the engine is idle, look at the data flow. It can be seen that the temperature at the downstream of the radiator is very low, which indicates that the coolant flow in the radiator is very small. The car is equipped with an electric control unit, which is an electric heating device on the basis of a traditional thermostat, so that the engine control unit can directly control the flow of the coolant. Remove the thermostat and fully heat it. The thermostat keeps on closing, indicating that it has failed. Troubleshooting: commissioning after replacing thermostat, confirm troubleshooting.