Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove diverter valve head from body

Measurement:

Observe the position of the spindle.
If the spindle is extended test between pins 2 and 3.
Expect approximately 6 - 8.5Kohms.
If the spindle is retracted test between pins 1 and 2.
Expect approximately 6 - 8.5Kohms.
If the spindle is not fully in one position test between pins 1 & 2 then pins 2 & 3.
Expect approximately 6 - 8.5Kohms.
Note:
1. Pin numbers are printed or stamped on the diverter valve head itself.
2. It is also advisable to check for any water leaks from the diverter valve body as these can enter the head and cause intermittent faults.