Frigidaire dishwasher won’t start (LED flashes instead)

I have a Frigidaire dishwasher model FDB1050REC2.

It's been working mostly fine for the last year. (Occasionally it doesn't start, but opening and closing the door and moving the dial to Rinse Only and back to Normal fixed that.)

As of yesterday, it won't start at all — pressing the start button causes the "Washing" LED to flash in approximately one-second intervals.

Things I tried:

• cutting the power to the dishwasher (via the circuit breaker)
• after restoring power, put the dial to Rinse only and pressed and held Heat Dry + Start/Cancel. Test mode did not fire.
• from idle, put the dial to Rinse only and pressed and held Heat Dry + Start/Cancel. Test mode did not fire.
• removing the front panel, disconnecting the two halves of the wiring harness and reconnecting

I tried cutting the power a few times, from a few seconds to a few minutes.

Documents:

• Wiring diagram: ftp://ftp.electrolux-na.com/ProdInfo_PDF/Kinston/154547901.pdf
• Manual: ftp://ftp.electrolux-na.com/ProdInfo_PDF/Kinston/154591101.pdf

I have a multimeter and other tools.