FARGO (AP) - A police detective has pleaded not guilty to drunken driving.

Fargo Detective Paul Lies was arrested Sept. 8 by the North Dakota Highway Patrol.

Lies, who has been with the department since 1989, was warned in March 2006 that further violations of the department's code of conduct could lead to his firing.

The letter of reprimand followed a New Year's Eve incident at a West Fargo bar. Documents from an internal investigation say Lies displayed conduct unbecoming an officer and violated the department's alcohol beverages policy.

The department's internal investigation into Lies' DUI arrest is ongoing, and could lead to his firing, said Lt. Tod Dahle.

Lies, 43, once was named police detective of the year. He also once was suspended without pay for two days for violating department rules regarding the processing of property and evidence.

Lies said in an interview that he had "made mistakes in my personal life."

"These incidents are not an accurate reflection of who I am or my life's work," he said. "I look forward to putting these things behind me and continuing to serve the citizens of Fargo."

His next court appearance is scheduled for Jan. 2.