But Toyota executives said the fire, which occurred during a private test run at Fuji International Speedway, was unrelated to the car’s adoption of hydrogen fuel instead of gasoline.

The cause, the company said, was a pipe joint loosened by vehicle vibration.

“What I want everyone to understand today is that hydrogen was not the cause of this problem,” Tomoya Takahashi, president of Toyota’s Gazoo Racing Company, said at a briefing.

“Rather, it is as the insufficient consideration of our design work,” he said. “Whatever fuel we used could have leaked and caught fire.”

Despite the setback, Toyoda himself ordered the team to continue working on the liquid hydrogen combustion technology, Takahashi said. The company wants to have the car ready for the next endurance series race in late May. That race will be a 24-hour run at Fuji Speedway.

Toyoda also would not let the incident deter him from buckling up in the vehicle. “He will continue to drive this vehicle because he is determined to show the safety of hydrogen,” Takahashi said.

The leak happened near the engine, and the hydrogen ignited because of the heat. A failsafe leak sensor automatically shuts off the hydrogen supply, forestalling a wider fire.

The pipe joint may have loosened partly because the liquid hydrogen drivetrain weighs about 300 kilograms (661 pounds) more than the gaseous hydrogen system, aggravating the vibrations. About 100 kilograms (220 pounds) of that weight is due to additional safety equipment. The joint segments are also replaced after every race, opening the possibility of an installation error.

Toyota is still having trouble shooting the root cause and remedy, Takahashi said.