Bottas was running second in the race when he started complaining of losing power. Very soon the Finn was called in and retired with a suspected MGU-H problem.
After Lewis Hamilton won the race, he extended his lead over Bottas to 69 points, essentially making it almost impossible for the Finn to catch up.
Mercedes Motorsport Strategy Director James Vowles explains what happened.
“At the end of the [Virtual Safety Car] period Valtteri complained of a lack of power,” Vowles said in Mercedes’ post-race debrief video.
“We could see on the data that the MGU-H, the hybrid element of the car that produces electrical energy, but also turbo control, wasn’t working correctly.
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“We tried a few switch changes with Valtteri which may bring these systems back, so through the steering wheel he could put a default code in that may bring back parts of the hybrid system.
“It was clear though that it had failed completely even after the switch changes and as a result we boxed the car and stopped it.”
Vowles adds that keeping Bottas on the track could have further damaged the engine, requiring it to be replaced, which would then trigger a grid penalty for the Finn.
“We felt that the system failure wasn’t hardware but actually electronic and the sooner you stop it the less damage you are going to do to any of the systems and the more chance that we will take no penalties with Valtteri as a result.
“We’ve got a lot of checks to do and we will check the systems in Portimao but hopefully no further penalties will come as a result of this failure,” concluded Vowles.