If the drawer isnt opening during the cycle then its nearly always the dispenser unit itself at fault here.
What you need to do if checking yourself is remove the outer door panel.
From there you will see the back of the dispenser unit. Check the wiring block is fully pushed on there.
If it is then you need a multi meter. Disconnect the wiring plug and test the coil on the dispenser and check the reistance of it. Its usually round 7K ohms.
If faulty then you need to replace the complete dispenser unit and that should cure the fault from there.
But if the dispenser and wiring are both ok then the control unit will be the fault not sending the power to the dispenser coil to open it.
So check that if you can as most of the time for this fault you have its the dispenser unit itself that causes this kind of fault.
If you need anymore info just get back to me.
Your very welcome Geoff.
Just wondering how you got on with the dishwasher as the question is still open?
Do you still need help on this?
If not then if you could rate the answer then it will close the question down.