Django Unchained actress Daniele Watts had initially claimed police actions last September were racially motivated.
Watts was handcuffed and briefly detained during the incident, after LA Police responded to a call about "indecent exposure".
Prosecutors made a deal to drop charges of committing a lewd act in public.
Watts - who played Coco in Quentin Tarantino's Oscar-winning 2012 film Django Unchained - and her boyfriend Brian James Lucas have been ordered to issue a written apology to three LA police officers.
They also pleaded no contest on Monday to disturbing the peace with loudness.
Lou Shapiro, a lawyer for the couple, said Watts will apologise for her comments but is not admitting she and Lucas engaged in lewd conduct.
He added she "wishes she hadn't said some of the things she said" to police during the incident.
According to the LA City Attorney's Office they will also have to carry out 40 hours' community service.
The pair had been facing up to six months in jail and a $1,000 (Â£659) fine if convicted of committing a lewd act in public.
Police were called to the Studio City neighbourhood of north Los Angeles on 11 September last year, after a report from a passer-by that a couple were exposed indecently inside a silver Mercedes with the door open.
Both Watts and Lucas, who is white, insisted they were only showing public affection and that nothing improper had been taking place.
At the time Watts took to her Facebook page to complain, claiming her rights had been violated when she was briefly detained after refusing to show ID.
In audio footage of the encounter obtained by the TMZ celebrity website, Watts appeared to allege the police were called because she was black and her boyfriend was white.
The officer was then heard questioning why she had played "the race card" and insisting he had the authority to request she provide identification.
An LAPD spokesman said US citizens are required to identify themselves if requested to do so by an officer who has reasonable suspicion to believe an offence may have been committed.
An actress investigated by police after a report she had sex in a car in public must apologise to officers, after admitting disturbing the peace.