John, I am having a similar issue with my LG dishwasher giving an OE error. I went through a lot of diagnostics and all plumbing looks good. I concluded that the height position of the drain pipe/air gap assembly is the issue. But this dishwasher has been installed for 5 years without a problem. Sink has a p trap (no s trap). But somehow now it gives the OE error. But if I drop down the air gap/drain pipe from the sink counter to under the sink then no problem.
I did take the dishwasher out and by moving the drain hose higher and lower I can see a big difference in the amount that drains. So my conclusion at this time is the pump is not working 100% and cannot push enough water through with the hose is in the higher position. I cannot change the hose position/air gap at the counter level. So seems like the pump performance must have changed.