Sheriff's Civilian Director Natalie Salazar, the head of the sheriff's Community/Law Enforcement Partnership Program, was tested two hours after the arrest and registered a blood-alcohol level of 0.20.
Multiple 911 calls reported a car stopped in a middle lane of the 210 Freeway in Pasadena Friday night.
California Highway Patrol officers found Salazar passed out in her county car with her head on the steering wheel and foot on the brake while the car was in drive.
Salazar was convicted in 2009 for driving under the influence of alcohol. She remained in her position at the department.
Sheriff's Dept. spokesman Steve Whitmore said Salazar has been placed on leave.
City News Service contributed to this report.