Engine Cooling Fan Problem

[a8pete]

I have a 2004 Audi A8 D3 4.0 TDI

As soon as I turn on the ignition the high speed engine cooling fan switches on and stay on.

Running the VCDS I get the following error:

18080 - Coolant Fan Control 1
P1672 - 000 - Open or Short to Ground
Freeze Frame:
RPM: 651 /min
Torque: 105.3 Nm
Speed: 0.0 km/h
Duty Cycle: 9.9 %
Voltage: 13.45 V
Duty Cycle: 9.9 %
Duty Cycle: 9.9 %
Temperature: 54.9°C

Anyone else had this problem and found a cure?
Any tips for hunting down the cause?

Many thanks