What are the odds to get the right codes and access to the secret room in Diamond Heist?

Solution 1:

For the first point, I'm pretty sure it's totaly random (and the odds are pretty weak). Here's what Payday's wiki says about that:

Now you head down to the bottom floor and enter a code, which fails most times to work (works 5-10% of the time). If the code does not work, the alarm will sound immediately and there is no longer any point to staying quiet then you will need to start searching for the CFO. If it does work, you can easily get all the diamonds without breaking a sweat.

However, from my experience, 5-10% seems a little too low; I'd rather say 20%. But maybe I've been lucky on this.

For the second point, I have to admit that I have no idea and can't find any good information about it. Each player seem to have his own theory; personally I think it's completely random. Sometimes, I did everything perfect (playing on overkill, get the 3 alarm boxes and the 10 gems without getting noticed, open the safe at the first try, don't break any glass anywhere) and the door wasn't there; just a brick wall.