Test sequence

Disconnect 4-pin harness connector from coolant Fan Control (FC) thermal switch -F18- located on lower coolant hose (bottom right).
Switch ignition on.
Bridge terminal -1- and terminal -2- of harness connector using auxiliary cables from VW1594.
- Coolant fan -V7- must run on 1st speed
Fig 1: Identifying Coolant Fan Control (FC) Thermal Switch -F18- 4-Pin Harness Connector Terminals
Courtesy of AUDI OF AMERICA, INC.
Bridge terminal -3- and terminal -4- of 4-pin harness connector using auxiliary cables from VW1594.
- Coolant fan -V7- must run on 2nd speed
If 1st or 2nd fan speed does not run:
Locate and repair open circuit using wiring diagram.
If no open circuit can be found:

Fig 2: Identifying Coolant Fan Control (FC) Thermal Switch -F18- 4-Pin Harness Connector Terminals
Courtesy of AUDI OF AMERICA, INC.
Replace coolant fan -V7-.