Thanks for taking the time to answer me.
I did some others tests, and this became much weirder. So, I removed all the code about the LED display, and still not working (value stay on 0). So I tried connecting the LED display to see how it react, despite the fact there was no code about it. When I plugged the power and ground wire on their respective pin on the Stalker, and one of the two (CLK or DIO, doesn’t matter which) on DIGITAL PIN 9, sonar reads corrects values again… The 4LED does not show any value (of course, no code was written about, and wires are not all connected), but the sonar works..
So I tried something else. I removed the 4LED module, and wired the 5vcc Stalker pin directly to the DIGITALPIN 9. Sonar works and read correct value. Thing is, I don’t know why it works that way. I tried on other digital pins, and it doesn’t work. It’s only on digital pin 9. Is it possible that some trash code is left somewhere on the Stalker and it somehow wait to get signal on DPin 9, or do I have a Stalker that is messed up ?