Blakers,
I do get the P0606 code with my VA duration box but I don't think it is random. I can throw the code at will by turning th box to 100% and doing one hard run. I normally leave the box on the 50% setting and have done several hard runs and never gotten the code. All it takes is a flip of the switch and planting my right foot down to see the P0606 return. Not sure if you have a way to clear the codes and see if it is the same for you.