1. Do the ECM reset procedure.
2. Start the engine.
3. Turn on headlights

If code P1297 is still indicated you have to check for a short in the wire. Measure voltage between body ground and the ELD 3P connector terminal No.3.

If there's appox. 5V you will need to replace the ELD. If not then you would have to check for continuity at the ECM side.

It's strange that you would have to leave the car overnight at the dealer. I'm sure they must take their time.

Check voltage between body ground and ELD connector terminal 1, with ignition switch on (II)and headlights off. Is there battery voltage?