This bulletin applies to all 2004 and newer Volkswagen vehicles with electronically controlled cooling fans. The pin-out for an electronically controlled cooling fan is as follows:
1. Terminal 30 battery power.
2. Key ON power.
3. Pulse with modulated (PWM) control signal from ECM.
Duty cycle of PWM control signal from the ECM determines fan speed. For example, key on is 25%, low fan speed is 50% and high speed is 75%.
When the fan control module has key on power, it must receive a PWM control signal from the ECM. If the control signal is not present with key on power, fans will run constantly.
Early vehicles such as the Tourag, Phaeton and W8 Passat will run the cooling fans at all times when a cooling system fault is present in the PCM.
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