Police say the suspect, driving a black and white Ford Crown Victoria, waved a bright spotlight back and forth across the victim's vision, giving the impression he was a police officer.
The Stanton resident pulled over, and the man dressed in a uniform asked for her driver's license and told her to step out and sit on the back of her truck.
"He began a conversation which was very peculiar," said Sgt. William Kohanek of the Buena Park Police Department. "Asking about personal life, asking if she had a boyfriend."
The suspect detained the woman for up to six minutes.
"He began touching her on the leg over her clothing but in a sexual manner. That was enough for her to try to get away," said Kohanek.
At that point, the radio in the suspect's car started making noise, and he got in his car and left.
Police describe the suspect as 30 to 35 years old, 6 feet to 6 feet 2 inches tall with a muscular build. He wore a blue, short-sleeved uniform with only one arm patch and a security-style equipment belt without a gun.
Police say that a real officer should have a full uniform and an identification tag. While the suspect had a badge, the victim wasn't sure if it looked legitimate.
Authorities warn women that during a traffic stop, the police vehicle should have a forward-facing, solid, red light.
The suspects' car had only the spotlight.
Police say the man may work for a security company and this may not be his first time doing this.
"What I'm more concerned about is he may try it again, and who knows how far he'll go next time," said Kohanek.
The woman did not call police until she returned home. She was not injured.
Police are asking anyone with information to call the Buena Park We-Tip hotline at (714) 562-3847.