Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the connector from the diverter valve
Disconnect ST17 connector from the right hand side of the PCB

Measurement:

Check harness for continuity across all the wires between the PCB connector and the diverter valve motor.
Also check the harness for good general condition.