Dropping out of the top ten with two laps to go, Honda have revealed a “caution from our high-voltage system” prevented Toro Rosso from bringing Alex Albon in for a second pit stop.
Albon, who qualified ninth for the British Grand Prix, started Sunday’s 52-lap race with the intention of making it a two-stopper.
He came in for his first pit stop on lap 13 and was expected to stop again later in the race.
However, an issue with his Honda engine meant Toro Rosso couldn’t risk pitting him as the car would not be safe unless completely switched off.
P10 with two to go, Albon fell to 12th at the chequered flag.
Honda F1 technical director Toyoharu Tanabe told Motorsport.com: “We had a caution from our high-voltage system. We will investigate exactly why it happened, from now.
“If you have some caution from the high-voltage system you need to turn the engine off to touch the car.
“Which is better – you keep running, or stop and turn the engine off to change the tyres? The compromised answer which we and the team made was to stay out.”
Albon’s marathon second stint was almost 40 laps with the Toro Rosso driver saying he could “see the carcass coming off” at the end.
“Another lap and we would have ruined the tyres,” he said.
“I still think our pace was good. It’s just we were on very old tyres.”