If you received a probation before judgment on a driving under the influence charge, you will not be eligible for expungement of the charges. If you received a probation before judgment on a different change you will have to wait until the later of 3 years after the entry of the probation before judgment or expiration of the probation.
You should consult with an attorney to determine whether you qualify for an expungement.
Regarding your question of whether a DUI can be expunged in Maryland, the answer is no because you got a PBJ.
The statute in Maryland regarding expungement (Md. Ann. Code, Crim. Proc. Art. 10-105(a)(3)) expressly excludes drunk driving charges (Md. Ann. Code, Transportation Article 21-902) where a PBJ is received. DUI charges cannot be expunged.
This statute outlines when and how an expugement may be received on other eligible charges.
No, PBJ for DUI means that your DUI cannot be expunged. The statute on same does not permit it and the reason is because the State wants to know if you have had a prior "bite at the apple" in case you happen to get another DUI infraction down the road. Sometimes if a DUI charge is amended to a lesser offense like negligent driving, you may be able to get it expunged, but even that can be tricky.