First, the electronic fan is rotating at low speed frequently, and the high speed normal 1. malfunction phenomenon. (1) the coolant thermometer pointer can not reach the normal working temperature for a long time. (2) engine power is insufficient and fuel consumption is increased by 0 (3). (the engine has been in high speed and speed. 2. main causes of failure (1) short circuit fault on line. (2) the relay switch contact is often closed. (3) relay control coil to short circuit fault. 3. Fault diagnosis is based on the common fault phenomenon of low speed and normal speed. Through the principle of drawing and drawing, we can conclude that the fault is in the low speed fan control circuit and the fan power supply circuit, which is independent of the high speed control circuit and the working circuit. The switch is first connected to the ignition switch. It is found that the electronic fan is constantly rotating, and the diagnostic instrument is used to see whether there is a cooling fan relay control circuit fault code. If there is, pull off the relay 12, use the test lamp to connect the 85 and 86 terminals of the relay 12, open the ignition switch and the test light is not bright (if it is bright, the relay coil circuit is short circuited by the relay); if it does not exist, the relay is directly pulled out of the relay 12, and the fan continues to rotate (if the turn is stopped, the relay switch contact often closed). Turn on the ignition switch and use the multimeter to measure the 12V voltage at the 30 terminal of relay 12, indicating that the line is short circuited with the power supply. Figure 1 is the cooling fan control circuit. Two, electronic fan low speed normal, high speed no turn 1. failure phenomenon (1) coolant temperature exceeds normal working temperature, pointer to red area. (2) the engine is rough, unable to accelerate and increase emissions. (3) the effect of air conditioning and refrigeration is poor. 2. main causes of failure (1) failure of fuse and relay power supply line. (2) the failure of the fan control circuit. (3) the relay 9 and 10 are damaged at the same time. 3. the fault diagnosis step is based on the failure phenomenon of low speed normal speed and high speed, and we can draw the conclusion that the fault is not related to the low speed control line and the working circuit by the fault in the high speed relay control line. Turn on the ignition switch, perform the low-speed connection with the fault diagnosis instrument, and the left and right fans operate at low speed. When the high-speed fan is connected, it is found that the left and right high-speed fans are not running. Use a fault diagnostic device to see if there is an electronic fan relay control circuit fault code. If yes, check the fuse 21 for fuse 21, pull off the relay 9 and 10, use the multimeter to detect the 86 end of the relay 9 and the 85 end of the relay 10 to the normal voltage (if 0V, indicating that the relay supply line has a circuit breaker). 2 test lamps are inserted into the pins corresponding to the control coil of the relay 9 and 10, and the high-speed operation of the fan is performed by the diagnostic instrument, and the test lamp is not bright. It shows that the relay to the PCM section has circuit breakage (if 2 lights are lighted, 2 relay is damaged simultaneously). Three, case analysis 1. failure phenomenon one equipped with V6 3.0L engine of 2003 Buick Junwei car after the driving of 137 thousand km, often the coolant temperature is too high, and when the temperature is high, the air conditioning is also not refrigerated. At high speed, it is not very obvious. When waiting for the traffic lights, it is particularly obvious. The pointer points to the red alarm area at once, but sometimes it slowly descends. When inspecting the repair shop, it was found that there was a crack in the cooling water tank resulting in insufficient coolant. No abnormal detection was found after the replacement of the water tank. 2. the cause of the failure should first be taken into account of the fan of the cooling system according to the failure phenomena and the description of the customer. Because only the fans of the cooling system will affect the refrigeration of air-conditioning. Moreover, the wind ahead can help the radiator to dissipate heat, which is enough to prove that the fan is out of order. The main reasons for the intermittent failure of the fan are as follows: (1) sensor fault; (2) PCM fault; (3) the relay contact ablation; (the insertion angle between the lead is loosened and ablated; (5) circuit short circuit and circuit breakage. 3. troubleshooting and eliminating all of the above reasons may cause intermittent fan failures, but not all possible components need to be inspected. Because many faults can be eliminated directly by fault phenomena and diagnostic data. The fault diagnosis device is installed according to the priority principle of fault code, and the power system on board diagnosis (OBD) system check is carried out, and no fault code exists. Turn on the ignition switch, start the engine and check the coolant temperature sensor, indicating that the temperature has exceeded 106 degrees. When the air conditioner is opened, the fan does not turn. At the same time, in the engine data flow, it is found that the low speed fan has been connected to the instruction, but the 2 fans are not running. According to the above phenomenon, we can directly eliminate sensor failures and PCM failures, indicating that the fault is in the fan circuit. First of all, the low speed relay is turned on with the fault diagnosis instrument, and 2 low speed fans are not running. When the instruction of the high speed fan relay is put on, the left fan is not running and the right fan runs well. According to the failure phenomenon combined with fan circuit diagram analysis, we can directly reduce the fault area by half. We can learn that the fault must be in the low speed control circuit, the low speed fan circuit (from the fuse 6 to the right of the fan motor) and the left fan high speed circuit. Check the low speed control circuit: (1) pull off the relay 12, use 1 good test lights to connect the 85, 86 terminals of relay 12, open the ignition switch and use the fault diagnosis instrument to operate the fan at low speed and light the light. Explain the low speed control circuit well; (2) open the ignition switch, use 1 good wires to directly connect the 30 and 87 two terminals of the relay 12, and find that the fan is not rotated, then the relay switch contact corrosion failure can be excluded; (3) then the line of the fan is checked, first check the power supply circuit to open the ignition. Using the multimeter to detect the 87 terminal of relay 12 and the voltage between the iron lap of the relay is 12V, the power supply is normal; (draw off the left fan plug, use the fault diagnosis instrument to command the fan at low speed and measure the left fan plug B terminal and the iron lap voltage also 12V, the power supply is normal; (5) insert the left fan plug, pull down the C1 05 connector, using the resistance gauge of the multimeter to measure the off condition of A and B two terminals, 0.04 Omega as normal; (6) use multimeter resistance to detect C105's A and D two terminals, and find it a circuit breaker; (7) pull off relay 9, measure the connection between the A terminal of C105 and the 30 terminal of relay 9, and the result is infinity and dismantled. The results are infinity and dismantled The C1 connector under the fuse box of the lower engine compartment failed and found the fault point: the A10 pin of the C1 connector is ablated. Because the cost of replacing fuse box and engine harness is too high, we finally weld the pin. After the completion of the repair, the high and low speed fans are running normally and the trouble is eliminated. Four. When it comes to difficulties in maintenance, we should first understand the working principle, control mode and key points of the system, and find out the cause of the fault according to the corresponding analysis of the failure phenomenon. Then, according to the logic relationship of the system components, the exclusion method, the reflection method and the diagnostic equipment are excluded. In this way, it can save less time and improve work efficiency, but also improve its own level. At the same time, troubleshooting is also very simple and fast.