A group of firefighters taking the recent lieutenants exam dashed off to the bathroom to access the answer key on their cellphones, The Post has learned.

The alleged cheats, taking the promotions test at a Queens high school, clicked a link to pull up answers to all 100 multiple-choice questions via a website that states, “We are very confident in this answer key and believe it to be 100% accurate.”

About 2,300 firefighters took the exam on June 20.

The city’s Department of Citywide Administrative Services, which oversees the exam, and the Department of Investigation are jointly reviewing the possible cheating scandal after an FDNY supervisor was tipped off by an anonymous person, sources said.

“Somebody walked into the bathroom and saw these guys on their phone,” a high-ranking FDNY source said. “They were pulling up the test material.”

Cellphones and other electronics are banned during city civil service exams, but the hopefuls managed to slip the devices into the school undetected to gain an upper hand on their fellow Bravest, the sources said.

Somebody walked into the bathroom and saw these guys on their phone… - High-ranking FDNY source

Nothing was done to address the scandal that Saturday, but honest test-takers caught wind of the wrongdoing, a source said.

The FDNY’s Bureau of Investigations and Trials has “been made aware of” the complaint, the high-ranking source told The Post. However, the FDNY states it “has not received a complaint of cheating from anyone who took or proctored the exam.”

No one at the DOI or DCAS would comment on their investigation.

The sources said the review is complicated by the fact that nobody has yet named any of the alleged cheaters.

“They’re not going to go on a witch hunt,” an FDNY source said. “They don’t want the test to be tainted.”

It’s been about four years since the last lieutenants test. Roughly a third of test-takers get promoted.

The FDNY was blasted by a federal judge four years ago for hesitating to pursue allegations of widespread cheating on the city’s 2007 entrance exam.