Electric Fan
Vehicles with M62TU, S62 and M73 engines feature a viscous fan as well as an electric fan. The electric fan cuts in when the cooling capacity of the viscous fan is no longer sufficient.
The electric fan is activated by means of a power output stage directly on the fan motor. The motor control unit activates this power output stage by means of a square-wave signal with duty factors (variable pulse width) between 10 % and 90 % thus controlling the various speeds of the electric fan. Pulse duty factors less than 5 % and greater than 95 % do not trigger activation but rather they are used for fault detection purposes. The power output stage features its own positive and ground supply.
The fan speed is influenced by the coolant temperature at the radiator outlet and the pressure in the air conditioning system. The fan speed is reduced as the vehicle speed increases.
If a fault occurs during operation a corresponding fault code will be stored in the fault code memory of the DME control unit.
For the purpose of checking operation and troubleshooting, the diagnostic program offers the option of activating the electric fan directly via the DIS tester/MoDiC.
Electric Fan DDE 4.0
The DDE control unit activates the electric fan by means of a square-wave signal with duty factors (= variable pulse width) between 5 and 90 % and thus controls variable speeds of the electric fan. The electric fan features its own positive and ground supply.
Troubleshooting
The activation function is monitored for short-circuit and open circuit but not the fan motor itself. Fault code 0480 "Electric fan" is stored if a defect occurs.
Consequence: Engine temperature increases
The fault code entry "electric fan, short to ground" may be caused by a mechanically blocked fan motor (in winter by frozen condensation water).
Note: As from 03/00 mechanical blocking of the fan will be detected as such and the type of fault “Electric fan mechancially blocked” will be stored.
Specified values, pressure sensor
Data on working range and substitute values.
The pressure sensor receives a 5 volt power supply from the control unit for the heating/air-conditioning system. The sensor signal is evaluated with the help of tables and forwarded to the engine electronic via the K bus. In the process, the refrigerant pressure in the air-conditioning circuit is converted to a load torque and the required fan stage.
Refrigerant pressure-fan stage conversion table
Each fan stage that is determined is transmitted via a telegram from the engine electronics. Prerequisite is a speed less than 80 km/h.
Pressure in bar _________ Fan stage
8________________________0
9________________________1
11_______________________2
13_______________________3
14_______________________4
15_______________________5
16_______________________6
17_______________________7
18_______________________8
19_______________________9
20______________________10
21______________________11
22______________________12
23______________________13
24______________________14
> 24____________________15
Electric fan DDE 5.0/5.1
The DDE control unit activates the electric fan by means of a square-wave signal with duty factors (= variable pulse width) between 5 and 90 % and thus controls variable speeds of the electric fan. The electric fan features its own positive and ground supply.
Troubleshooting
Faults in the control of the electric fan and on the fan itself are monitored. The following faults can be stored:
- 41F0, Activation short circuit to positive
- 41F1, Activation short circuit to earth
- 41F2 Activation circuit break
- 41F3, Excess temperature output stage
- 4B20, 4B22, Electric fan jammed
Consequence: Electric fan not functioning, engine temperature rises