Mercedes says a turbo defect it has never encountered before led to Valtteri Bottas' engine failure at the Spanish Grand Prix.
Bottas was running third in Barcelona when the engine issue occurred, forcing him to retire from the race and costing him valuable ground to Sebastian Vettel and teammate Lewis Hamilton in the title fight. Mercedes had been forced to revert back to the power unit Bottas had used at the opening four races of 2017 when it detected a water leak in his new power unit ahead of FP3.
Though Bottas was running an older engine, Mercedes has revealed a defect led to the failure, with team boss Toto Wolff saying it is proof the team must remain "double diligent" in its fight with Ferrari.