Originally Posted by Jason Feuerstein

Sigh.

So after tearing apart the wiring harness under the dash, replacing the brake switch, and ultimately removing the shift interlock solenoid entirely, I sat back and thought to myself, "Jason, what if this is happening because you're an idiot?"

When I first got my Nanocom, I went in and changed a bunch of settings (superlock, single locking, etc.). Went back in this evening and there it was: Shift Interlock: NONE. Which, contrary to what I thought at the time, did not permanently disable the shift interlock, but made it so the BCU never sent a signal to deactivate it.

Lesson learned: Do more research before fiddling with stuff.