How can I find the keyless door lock code for Grand Marquis 2009?

The factory default code is stored in the ECU and can be retrieved with a high-end OBD scanner

It's on the left trunk hinge inside trunk

It's not in the trunk on mine, I've read that it's on the lock module inside the driver's door. I haven't removed the panel to get to it yet.

so what is the ECU

I think the Electronic Control Unit is inside of the driver's door, and should have the code on it. A dealer can retrieve your code with the VIN, for a fee.

Thanks to all. Not located on door panel or inside trunk. Had dealer to reset it with new one. $40+ fee from manufacturer, they said. Works great now.