Cooling fan, description and operation, E39
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Cooling fan, description and operation, E39
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Overview
The car is equipped with two cooling fans located behind the radiator. The cooling fans can be run at four different speeds:
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Speed 1 Both fans running slowly
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Speed 2 Both fans run at moderate speed
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Speed 3 One fan runs at max. speed
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Speed 4 Both fans run at max. speed
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The cooling fans have their own relay box and the activation command goes from the ECM via the SCM (Signal Conversion Module) and the UEC to the relays.
The fans are controlled by ECM through the following input signals:
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Fluid temperature from automatic transmission
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Radiator fan relay box (706) is supplied with +30 from UEC to pins 3 and 6, and is grounded to G30A from pins 5 and 2.
From the ECM, there are 2 lines to the SCM (Signal Conversion Module) for fan activation. The ECM earths the lines in 4 combinations (fan speeds 0, 1, 2 and 3). The request for fan speed 4 is received by the SCM from the ECM via a bus. From the SCM, there are 3 cables via a front fuse box to the relay box. These cables are connected to pins 1, 4 and 7 on the relay box. Depending on which connections are earthed, and the combinations in which the connections are earthed, the four different cooling fan speeds are achieved.
Fan control
The ECM from has 2 digital outputs which are used for fan control. The ECM has drive stages which earth the two 2 lines when they are active. The SCM reads the status from the ECM for fan off and the first 3 speeds. A bus message from the ECM is used for the top speed. The SCM earths the 3 lines to the relax box for the cooling fans (706).
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Power
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Fan off
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Stage 1
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Stage 2
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Stage 3
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Stage 4
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ECM-SCM
Pin B8
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high
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high
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low
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low
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low
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Pin B10
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high
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low
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high
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low
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low
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Bus signal
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off
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off
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off
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off
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to
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SCM Relay box
Pin A17
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high
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low
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high
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low
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low
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Pin A33
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high
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high
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low
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low
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low
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Pin A61
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high
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high
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high
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high
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low
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