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Auto electronic fan control mode and troubleshooting

by:TOCH     2021-02-26
Automobile electronic fan control mode and troubleshooting case analysis During the use of the vehicle, the engine will generate excessive heat. In order to prevent the engine from malfunctioning due to overheating, people have designed a cooling liquid circulating heat dissipation system in which the heat dissipation fan plays a pivotal role. Regarding the electronically controlled cooling fan, the control methods adopted by different models are not the same. Here are two examples of failures to understand the working principles and troubleshooting of the two common electronic fan control methods. Case 1: An Audi V62.4L displacement car. The cooling system of the car was 'turning on' because the electric fan did not turn, and the electric fan still did not work when the air conditioner was turned on. Two electronic fan cases The control of the radiator fan of this Audi car is realized by controlling the ground wire of the fan relay through the dual temperature thermal switch. The car’s cooling fan system has two electronic fans. The red wire in their connecting harness is the positive wire, the brown wire is the ground wire (fixed directly on the beam), and the red positive wire is a positive wire on the right beam. Fixed at the column. The control of the red positive wire is divided into fan low-speed relay, air-conditioning relay and fan high-speed relay control. Pay attention to their specific positions during maintenance. The fan low-speed relay is located in the third relay position in the fuse box on the right side of the engine, and the fan high-speed relay is installed in the No. 217 relay in the auxiliary fuse box under the driver's feet. The low and high-speed operation of the fan is realized by controlling the grounding of the relay according to the temperature of the coolant by the dual-temperature thermal switch on the radiator. When the air conditioner switch is turned on, the fan low-speed relay is controlled by the air conditioner fan relay to rotate the cooling fan. The ground wire (green/yellow wire) of No. 217 relay is connected to the dual temperature thermal switch. Once the coolant temperature rises to a certain temperature, the dual temperature thermal switch controls the relay to ground, and the cooling fan will enter a high-speed operation state. In addition, the main live wire and control live wire of No. 217 relay are powered when the ignition switch is turned on. According to the working principle of the car's cooling fan system, the car lacks a fan low-speed relay (users report that this car has been repaired in other repair shops). But after installing it, the cooling fan only has high-speed gear instead of low-speed gear. After careful inspection, it was found that the No. 217 relay was burned out, which caused the cooling fan to always be in high-speed operation. After the No. 217 relay was replaced, the fault disappeared. Case 2: In a Samsung Jielong car, the water temperature gauge shows normal temperature during driving, but if the engine is stopped and the engine is running at idle speed, although the water temperature gauge shows between 90 and 100°C, the cooling system is already 'boiled'. At this time, it was found that the cooling fan could not run at all. Engine high temperature alarm The control method of the cooling fan of this car is very different from that of the Audi car. The cooling fan of this Samsung Jielong car is controlled by the car computer. After inspection, the cooling fan relay lacks a control ground wire. When the engine is running at idling speed, the actual temperature of the coolant measured with a thermometer has reached 110°C, but the water temperature gauge of this car still indicates between 90-100°C. Use a multimeter to measure the resistance value of the water temperature sensor plug to about 100 ohms. Therefore, it is initially suspected that the water temperature sensor plug is damaged. When there is no substitute for the time being, find a 2k ohm sliding variable resistor in parallel with the water temperature sensor plug to reduce the resistance value. If the sliding variable resistor is adjusted at this time to make the temperature displayed by the water temperature meter consistent with the actual temperature of the coolant, the cooling fan will actually operate normally as the temperature rises. It seems that the cause of the failure is the water temperature sensor plug. Due to the damage of the water temperature sensor plug, it always gives the car computer a low temperature error signal that the cooling fan cannot operate, and the cooling fan naturally cannot operate normally. Finally, after replacing the water temperature sensor plug, the car returned to normal. It can be seen that the computer of this car receives the input signal of the water temperature sensor plug. When the water temperature reaches the specified value, the computer controls the ground wire of the fan relay to make the cooling fan run.
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