Symptom: the owner reflects the vehicle after running, the dashboard air conditioning control panel set the temperature to the lowest, the outlet still feel cool enough.
    Fault diagnosis: air conditioning pipe connected to the air conditioning pressure gauge, start running the engine, the automatic air conditioning temperature set at 18 ℃, observe the pressure gauge changes. Low pressure piping pressure down to 225kPa, high pressure pipe pressure rose to 1200kPa, indicating the compressor pull work. Touch the temperature of the air conditioning low-pressure line by hand, feel warm, and the temperature of the high-pressure line between the condenser and the evaporator, feel hot, but also see the electronic fan in front of the condenser is not running. Obviously, this high and low pressure pipeline temperature is too high the main reason is due to poor system cooling caused. As the high-pressure pipeline refrigerant pressure is low, in the first easy after the difficult test principle, first added 150g refrigerant, the results of high-pressure pipeline refrigerant pressure rose to 2000kPa or more, the pressure rise too fast is very dangerous So close the air conditioning, the maintenance ideas will focus on the electronic fan control lines.
    Connect the GT1 original diagnostic instrument, select the X system E53 chassis, enter the self-diagnosis main menu, double-click "IHKA automatic air conditioning heating and cooling system", enter the electronic control module, query fault storage, GT1 shows a windshield heating on the failure Information, which is not directly related to the failure of this case, clear the fault information, select "DME digital electronic engine servo system M72" electronic control module, query fault memory, GT1 display:
    (125) 7D tank outlet temperature sensor
    (098) 62 Fuel tank ventilation solenoid valve control
    (140) 8C according to the characteristic curve cooling control
    (141) 8D electronic fan control
    It can be seen that, in addition to 098 fault code information, the remaining three fault codes are related to the engine temperature control. Execute the clear fault information memory function, and the 4 fault codes are successfully cleared. To verify that the electronic fan is working properly, click on the "component execution" function to trigger the electronic fan action. GT1 is displayed in "Diagnostics", meaning that the electronic control module should not be provided for this function. Similarly, in order to observe the operating parameters of the electronic fan, click on the "diagnostic response" function, GT1 also shows "in the diagnosis."
    Due to electronic control module self-diagnostic function limited, unable to further test the performance of electronic fans, then click on the "function selection" button to view the relevant maintenance information files. Click "Engine Control" → "Regulator" → "Electric Fan" to enter the maintenance information database of "Water temperature sensor and electronic cooling fan". As can be seen from the circuit diagram, the component line connection is: the electronic fan plug for the 4-pin form, one pin is empty feet, the remaining three lines of two thick lines for the fan power and ground wire , Another black / green thin line and DME control module connected to the 4 feet for the fan control of the data line.
    Water tank outlet temperature sensor, it is a two-pin form of thermistor, located in the bottom of the radiator tank, the two lines are connected with the DME control module 38,39 feet, the signal data only for the electronic Fan control.
    In terms of working principle, since the M62TU, S62 and M72 engines are equipped with a coupler fan, the role of the electronic fan in front of the condenser is the auxiliary heat dissipation function. The fan and its power output stage (electronic amplifier) ​​are designed as a cartridge, so the DME control module can pass the black / green line with a pulse load parameter (duty cycle) between 10% and 90% of the rectangular wave to the fan speed For stepless control. While less than 5% and greater than 90% of the load parameters are used for fan failure identification. Eventually, the speed of the electronic fan is controlled by the coolant temperature of the tank outlet and the air conditioning refrigerant pressure, and gradually decreases as the traveling speed increases.
    Learn more about the operation of the electronic fan mechanism, the next detection method is very clear. Using the SUN engine comprehensive detector oscilloscope function, measure the black / green line signal output status, found to be a group of 12V rectangular wave. When the engine idling and air conditioning off conditions, observe the waveform duty cycle of 90%; open air conditioning, with the refrigerant pressure increases, the waveform duty cycle becomes 80%. In other words, the data line is a negative trigger in the form of fan speed adjustment. At this point, you can determine the fault in the electronic fan itself, replace the assembly, the fault completely ruled out.
    Fault Summary: Through the E53 chassis equipped with electronic fan understanding. Can feel the car electronic control technology continues to progress. The use of single data lines or bus data transmission to control the implementation of electrical components, will become increasingly popular, it has many advantages, and even the difficulty of detecting the fault will be greatly reduced, which is also on the Detection techniques and means of understanding.