It's the ambient temperature sensor, not the engine temperature sensor. My guess is that the head unit either contains the sensor or is responsible for broadcasting it. The head unit talks to the dashboard to redisplay nav instructions, I'm guessing it's also responsible for sending the temperature info to the dashboard. And since I pulled the fuse, all I get is --F, so the information isn't available on the CAN. Don't know why - I'm not an automotive engineer :)