I worked out this issue by using a current mirror. Basically, an NPN pair wired up to send a very small current to the LED, not enough to light it. The mirror output would swing enough voltage that it could be sensed with a GPIO. I did it this way as I didn’t have an ADC available. Once my diags were done I turned off the current mirror so even the phantom sense wasn’t present.

If you have an ADC, you could also just measure the FET drain voltage with the FET ‘off’. Toggle the FET on then off, then quickly sense the drain voltage afterward.  It will be 0 if the LED is unconnected, or about Vcc-Vf with the LED present, slowly making its way up towards Vcc as the LED bleeds off charge.

And finally, the easy way: use a low-threshold nFET like a BSS138 to watch the driver drain. Hammer the driver, check the FET state immediately afterward. If the FET stays off, no LED, if it turns on, LED is connected. Try it, here:

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![schematic](https://i.sstatic.net/NiY7Y.png)

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