Sent ECU away for testing and it came back OK
So, even though I tested the relay I got a new one and fitted it all back up. Got communication and the engine started - happy days !
But then I turned it off and now back where I was, no comms and wont start.
I must be looking at a wiring fault I guess. It has to be something I disturbed taking it on and off, but wiggle test not proving fruitfull.