Norcold refrigerator "NO FL" code, propane burns fine

Chris is correct. The spark wire becomes the thermocouple equivalent wire in newer systems. And the frame of the flame assembly is the ground. When there is a flame, that heat generates a small current, ~30 microamp as Chris said. That means any high resistance in that wiring can cause a misreading by the circuitry.

And the PM mentioned is spot on too...

Good luck, hope a good cleaning is all that's needed. Those boards aren't cheap if it's a bad board and not a contact or the electrode.