I just bought a 2007 scion TC.
I noticed that when i put the HU to show the temperature, it only shows -- F
Does this mean that the sensor is broken or there some other possibilities?
How do i check it?

This is my first car and i don't have lots of knowledge about this, so any help will be much appreciated. Thank you

 

That's part of the HVAC, not the head unit. And there's no way to know if it's a bad sensor or electrical issue with the unit itself. Try going to the dealer.

 

sounds like the sensor is either dead, or just has a wiring problem/connection. the sensor for the outside temp is in the front by the left side horn, i believe. check that wiring connection, sounds like it just might have corroded. also, its not the service port (H on the screw) for the a/c, but it's near all of that.

i did find the part number in case you need it. 88625-32171, it's about $40.