An NYPD detective who was shot over $20 while washing his car in Brooklyn in 1990 has died after spending more than three decades in a coma, law-enforcement sources told The Post on Sunday.

Officer Troy Patterson was just 27, newly engaged and off-duty when he was ambushed by three armed thugs looking for a few bucks outside PS 3 in Bedford-Stuyvesant.

The then-six-year department veteran — who had already racked up seven commendations for police work at the time — was shot in the head with a .38-caliber pistol during the botched robbery.

The panicked suspects fled after the shooting, leaving Patterson’s wallet at the scene.

The hero cop — who had been washing his car at a fire hydrant three blocks from his home when shot — remained in a vegetative state until he died Saturday night, sources said.

Patterson was promoted to detective in 2016.

The three suspects — Vincent Robbins, Tracey Clark and Darien Crawford — were later arrested in the unprovoked shooting.

Robbins, now 53, was convicted of assault and attempted-robbery charges and sentenced to a prison term of five to 15 years. He was released in 2000, state records show.

Clark, the alleged gunman in the shooting, also went to trial in the case. The outcome of the case is not immediately available, nor are any details of the charges against Crawford.

Although Patterson never regained consciousness, New York’s Finest never forgot the Brooklyn cop.

“We come here every year to honor his life, to celebrate his life to let his family and to let him know we will not forget,” NYPD Assistant Chief Judith Harrison said during a vigil for Patterson in January 2022.

“The Police department has a saying, ‘We will not forget,’ ” Harrison said. “But when we gather here what we do is we put action behind those words. So we’re here to celebrate Troy, we’re here hoping for a miracle more than 30 years later.

“We will never forget.”