Fault phenomenon: a Nissan G11 car with a total mileage of 43 thousand km, the cooling fan is running at high speed after opening the air conditioner, but the cooling fan will continue to run at high speed after the air conditioning is closed, and the cooling fan can not stop when the cooling fluid reaches 95 centigrade, and the cooling fan can not stop at high speed. Only the cooling fan can not stop at high speed. Only the cooling fan can not stop, only will the cooling fan run. Only the cooling fan can not stop at high speed, only will the cooling fan run. Only After the engine is restarted, the cooling fan will stop working. Inspection and analysis: check with fault diagnosis device and trouble free code storage. After analysis, ECM controls the cooling fan based on the speed, the temperature of the engine coolant, the refrigerant pressure and the air conditioning signal, so the pressure meter is connected to the air conditioning to test the pressure of the air conditioning. It is suspected that there is a problem with the cooling fan relay. After the replacement of the intelligent control module, the trouble remains. Since the cooling fan can start running when the coolant temperature reaches 95 degrees, the temperature signal of the coolant is normal. Because the air conditioning system can work normally, it shows that ECM can receive the signal of air conditioning connection. The rest of the air conditioning pressure signal is doubtful. The read data stream found that the signal voltage of the air conditioning pressure sensor is 2.201 V. while the normal data should be 1.304V, indicating that the signal of the air pressure sensor is really out of order. Elimination method: replace air conditioning pressure sensor.