The former Formula One driver did not request a B-sample and will be suspended from racing until a sanction is handed down.
The 36-year-old said he was “ashamed” after the test and admitted that his career was probably over now.
“Auto sport is perhaps over for me,” the Andretti driver told French sports daily L’Equipe.
“After the event I saw the guy who tests signalling me. There, in my head, I knew immediately. I knew it was over.
“I made a mistake, I’m guilty.”
The inaugural FIA Formula E championship — involving single-seater, electrically powered cars — got underway last September in Beijing. – Agence France-Presse