In pronouncing sentence, the court must consider, but is NOT bound by, the guidelines issued by the Pennsylvania Commission on Sentencing. The only limitations on the sentence that the court can impose are (1) mandatory minimum sentences, if applicable and (2) the statutory maximum for the grade and degree of the offense.
If the sentence imposed was the result of a negotiated guilty plea, then it is next to impossible to get it changed. If it was part of an open guilty plea, the remedy is to file a Post-Sentence Motion with the court asking for reconsideration of sentence. This must be done within 10 days of imposition of sentence.
No matter how it turns out, let's hope that your son gets the message and gets his life back together and becomes a successful and productive member of the community.
The court must consider the Pennsylvania Sentencing Guidelines when fashioning a sentence. A Second DUI with a BAC above .16% has an Offense Gravity Score of 5. With a prior record score of either 3, 4 or 5 being considered, 18 month is a minimum sentence within the standard range.