I suspect the use of the term "voltage drop" just shows he doesn't
understand. A drop will not necessarily make it quit working. Perhaps
his is simply saying that the power is not getting to the dishwasher.

You are going to have to get to the input wires and measure the voltage
there. Perhaps they are available at the bottom front of the machine.

Agreed ... it would be an unusual drop to keep it from working. However,
there is a heater in DWs. Sometimes, all one has to do is run the hot water
in the adjacent sink until it flows hot, before turning on the DW. But
that's in the case where the performance is sub-par but almost acceptable.

Measuring the voltage under load requires some fiddling around and some
knowledge.