is my temperature sensor f**ked up?

Well, after installation of audio system, I noticed how my temperature on the screen always shows somewhere around 7 degrees. Thought it was just a weather..

Well tonight, I am pretty sure it's way below than 11 degrees... when I start the car it was showing 11 degrees, as I drive, the temperature went down to 3-4 degrees. Is this suppose to be like this? or is the temperature suppose to be at around what it actually is when I start the car?

Only modification I have is 5 channel amp and speakers in front door, woofer, and T1R voltage stablizer..

Thanks in advance.