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 the 6 way 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 condiiton.