Techeetah has been fined €30,000 for adapting newly-introduced driver safety harnesses in Santiago, but has retained the first one-two finish for any team in Formula E history.
Jean-Eric Vergne survived a frenetic battle with team-mate Andre Lotterer to win the race and take the championship lead.
Both Techeetah drivers, along with Dragon's Jerome d'Ambrosio, were then placed under investigation, which ran until late on Saturday evening local time.
The stewards determined that the teams had made a "modification to the safety harnesses" issued for this race and "did not ask the technical delegate before adding these parts".
New harnesses were delivered to teams ahead of the first race to be run without a minimum pitstop time for the mid-race car swaps.
It was done to ensure drivers swapped cars and safely secured the belts with ease, as only the top belts have a sensor to confirm they have been sufficiently fastened.
Vergne's pitstop time was 46.847 seconds, the quickest of anyone, while Lotterer's was the third-fastest at 48.372s and d'Ambrosio's two seconds slower.
Techeetah was fined €30,000 across its two drivers, while Dragon was fined €15,000, all of which must be paid to the FIA within 48 hours.
One theory is that the teams added a makeshift handle to the lower strap that made it quicker for the mechanics to tighten safely.
Techeetah team principal Mark Preston said the FIA's wording suggested there was a "grey area".
"We have two LMP1 drivers who are very experienced in the world of fast pitstops," he told Autosport.
"Everyone has to agree what's allowed and what's not.
"It's not a modification for safety, it's a matter to make sure you can do the belts up quickly - it's for practicality, let's say.
"It was a hard one for everybody in the discussions."
According to the stewards, the FIA's technical and safety departments will clarify "what, if any, modifications are permissible in respect of the safety harnesses" before the next race in Mexico on March 3.
As the race result stands, Vergne retains his five-point lead over Felix Rosenqvist in the drivers' championship and Techeetah keeps a slender two-point advantage over Mahindra in the teams' contest.