Diplomat dishwasher adp 8332

First time I’ve posted anything-so please help.
I have followed the many posts about these dishwashers and have decided to tackle the problem we have with ours so I’m sure from what I’ve read someone will be able to help. (We haven’t used the dishwasher for months because of this fault) The appliance is 5 years old and displays the F4 fault. I have cleaned the filters and the outlet waste pipe. The black grill at 3 o’clock in the sump was particularly dirty and I have gently -with a small paint brush- cleaned that too.
I restarted the machine in rinse mode (only because I didn’t want to wait too long) and at the end of the cycle it worked then I did it again for luck! Job done I thought! Then I tried a the short 30min wash cycle. At the end of this the F4 fault reappeared .
I removed the appliance from it’s place and took the side off there is no evidence of anything suspicious or leaking under there. With the appliance out I disconnected the waste hose and put it into a bucket and ran two successful rinse cycles, water and a small amount of food debris came out. Then I put the machine back and reconnected the outlet hose to the sink trap and tried the 30 min wash cycle again and the fault came back In all cases the sump inside was totally empty of water and the pump continued to run until I switched the machine off. I suspect some sort of level detector which should switch the pump off and end the cycle is faulty?
Getting desperate now please help!