Ernest Azoadam was on the bus with friends on Feb. 15 when police responded to a call about a teen in medical distress at a gas station.
Azoadam was taken to hospital, where he was pronounced dead.
Police said later that evidence of alcohol was found on the bus.
But the coroner's service has now confirmed that toxicology results did not identify any alcohol, drug or medication that would explain Azoadam's death.
The coroner is continuing the investigation.