Joe Simpson is seen departing ABC GMA at Streets of Manhattan on March 15, 2010 in New York, New York. Credit: Soul Brother/FilmMagic

Joe Simpson says he's not guilty for driving under the influence.

The 54-year-old father of Jessica and Ashlee Simpson pleaded not guilty Thursday to two DUI charges, E! News reports.

Simpson was arrested on Aug. 4. in Sherman, Oaks, Calif. after officers believed he was intoxicated. An LAPD spokesperson told Us Weekly, "He was detained overnight at Valley jail in Van Nuys before being released at 9:40 a.m. on August 5 after posting $5,000 bail."

Simpson had his lawyer enter his not guilty plea on his behalf Thursday, and a pretrial hearing has been set for Oct. 11.

The grandfather of Ashlee's son Bronx, 3, and Jessica's daughter Maxwell, 4 months, could face a maximum penalty of six months in jail, three years of probation and a $1,000 fine if convicted.

"Joe's arrest shocked his family," a source told Us. "Anytime he's in the news, it directly reflects upon Jessica and Ashlee."