Hello,
I use my Arduino for reading my temp sensor, but's now oudside my car, so the sensors ground is connected to the GND pin on my Arduino.
In my car the sensor with connecto to the car it's ground from the battery.
Can I connect the cars ground to the GND pin of my Arduino or will this break it?
You need to provide a schematic showing what you currently have. In general, most stuff will be referenced to the car ground system and anything I build would share a ground with the car ground. That said, we need to see just what you have to make sure - if you are reading a temp sensor that is on the engine (an existing one) then you are probably already referenced to ground.
If at all possible don't connect any sensor to vehicle chassis, always take the ground from the wire
back to the Arduino - otherwise your sensor is just going to be picking up voltages caused by
ground currents from the various lights and engine (you'd have a ground loop). Yes you share
ground with the vehicle, but at one point only, usually the supply.
Hello,
I created a image, the one at the top is now, the one below is what I want.