ECI sounds like a good tip, however, I went to their site and I see every brand of electronic elevator component there except for TK. I wonder if they call it something else.

In cycling the unit perhaps 30 times, we finally got the E2 code to reappear.

We've replaced 2 DZ relays on the main board as suggested. Since the trouble was intermittent, it may take a while to see if this does it.