[Bill Leonard]

What constitutes a pit stop? Can I simply drive through pit lane? Do have to stop at my station? Do I have to load up a nominal amount of gas, change tires, repair damage? What if I have to pee? Thanks. [Forget the last - I don't have DLC for that.]

[Simon Meisinger]

You have to stop and do some kind of work on your car.

Adding 1l of fuel would be enough, for example.

[Peter Mathen]

I was DQF today in my first race because not fulfilling my pitstop (even I was sitting 1 minute in the box), as this was also my first pitstop in AC. I stopped in my pitbox, changed the number of liters for fuel but nothing happened.
After that I tried the pitstop myself in a AI race and now I know I must set the changes in the pit menu before I enter my pitbox (I didn't know that because in RaceRoom you can change setting in your pit and confirm it with a button press).
In YouTube someone showed if you forget to set the changes beforehand, you can simply drive a few meters back and enter your box again then the changes will also be made.

I think the next race with a pitstop will be surely no problem for me  

Peter

[Neil de Guzman]

if you just park in front of your pit and did not do anything to your car, then it doesn't register as a pit stop. Like the comment above, you need to add fuel at least a liter and you're good to go. You can change your tyres too, and pee while your crew works on your car. You have more or less 30 seconds to pee if you're serious about it...