You can read the Analysis which states the penalty on the MD General Assembly site: http://mgaleg.maryland.gov/webmga/frmMain.aspx?pid=billpage&stab=02&id=HB0011&tab=subject3&ys=2017rs
I don’t know how it will be enforced (can someone be pulled over for this, or is it an additional thing like seat belt/cell phone use), but I do see the following text in the Analysis document:
The driver of a diesel vehicle must obey any sign or direction of a police officer to stop the diesel vehicle and submit to an emissions test administered by an emissions inspector in specified circumstances, or at any location or time when a police officer has reasonable cause to believe that an individual diesel vehicle is violating emissions standards established under the program.