Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect plug from diverter motor

Measurement:

Check for continuity (zero resistance) of the blue, black and brown wires running between the main PCB (pins 5, 6 and 7 of X3) and the diverter valve.
Inspect the harness and connectors for good overall condition.