Jean-Eric Vergne's fire during qualifying for the Japanese Grand Prix was caused by his Toro Rosso's rear brakes not releasing properly.
The Frenchman was forced to pull off at the exit of the hairpin in Q1 after both his rear-left and rear-right brakes caught fire.
This is understood to have been caused by the rear brake system retaining hydraulic pressure even when the driver was off the brake pedal, although why this happened is yet to be established.
The problem is not related to the front brake issue that forced both cars to retire from last week's Korean GP, which was traced to a brake duct problem.
"All we know is that the brake pads got stuck, both on the right and the left and it caught fire," Vergne told AUTOSPORT.
"It is may be something in the [braking] system, we are not sure at the moment and the team is investigating."
Vergne is confident that that the fire that resulted from the brake flames igniting the bodywork has not done any more serious damage.
He ended up 18th fastest in Q1 based on his run on hard-compound Pirellis and will start 17th thanks to Adrian Sutil's five-place grid penalty.
"Hopefully the gearbox is fine and I'm quite confident that I'm going to start the race from 17th position without any problems with the car," said Vergne.
"Yesterday was really hard with my car, we worked a lot with my car and it was going to be a lot better in qualifying because I was on a good trend.
"The laptime with the prime was not representative because I made a mistake on that lap and I knew I would improve a lot on the option.
"It's a shame because with my car we had the opportunity to do well."