Battery problems have prompted the grounding of another Boeing 787, one year after a similar issue led to a months-long global suspension of the jet's flights.
Japan Airlines reported that a mechanic saw white smoke rising from beneath the cockpit of a parked Dreamliner during routine maintenance at Tokyo's Narita International Airport on Tuesday.
An investigation found one of the eight cells of the plane's troubled lithium-ion battery had leaked. It said a safety valve meant to release excess pressure had worked properly and that it did not catch fire.
JAL replaced the plane with another Dreamliner jet, and said it will keep flying its other 787s following routine maintenance checks.
The worldwide fleet of 50 Dreamliners was grounded for more than three months last year after battery problems sparked a fire in a parked plane and forced the emergency landing of another.
Boeing later rolled out modifications to the battery, but admitted it did not know what caused the meltdowns.
The U.S.-based multinational company said the modifications appeared to work as designed in Tuesday's battery incident in Tokyo.