Probation can be difficult to second guess. It has a whole arsenal of possible sanctions available to them, ranging from a wrist slap (more intensive supervision, more reporting requirements, more random alcohol tests) on the one extreme to house arrest or revoking probation outright on the other.
What they will do in your case will depend on many factors, such as your background and history and the facts and circumstances of the underlying case, how well you've been getting along with your probation officer, whether you've been in good over all compliance with the terms of his probation before the violation or whether you've given them trouble before (and how much of it).
These aren't all of the measuring sticks that will help probation to decide how to handle your breath test results, but you get the picture. It will all come down to whether probation thinks that working with you will ultimately turn you into a successful probationer and a productive citizen or whether they think you never will get the message and will want to wash their hands of him.
In my experience, probation understands full well that sometimes a probationer who is not supposed to be drinking will relapse and that alcohol detecting devices do have margins of error. Also, this is a technical violation. That is, it did not result in a new arrest. So it would be atypical for probation to give up on you altogether at this time for this type of a first violation.
If a violation is lodged, however, you will be entitled to a hearing. You should notify your lawyer at that point so that if probation and the DA are asking for revocation and resentencing to jail, someone can put forward all that you have accomplished during the past year and make a good argument for his continued liberty or, in the worst case scenario, for house arrest rather than incarceration.