A video showing the error mode, and the output of the wheel speed sensors.

The short version: The wheel speed sensors read properly and agree with each other, but intermittently jump from the actual speed to numbers in the minus 600 range. I'm thinking this may just be a glitch in the Autophix device, but can't be sure (it's not causing any other issues with the car, so apparently isn't a problem).

UPDATE: Got the new switch today, but a couple days ago, the problem just went away as abruptly as it appeared. I'm going to wait until it comes back (if it comes back) to replace the switch so I will know whether that was the cause of the original problem or not.