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Valtteri Bottas led for Mercedes on the morning of the second day of Formula 1 testing at the Bahrain International Circuit on Wednesday, only to suffer a setback when he caused a red flag just before lunch.

Three days after seeing his hopes of a maiden F1 win from pole be dashed by a tyre pressure issue, Bottas returned to the wheel of the Mercedes W08 car in Bahrain as teams continued their in-season running.

Bottas turned in a fastest lap of 1:31.771 on Wednesday morning to top the timesheets for Mercedes, finishing three-tenths of a second clear of Force India's Esteban Ocon.

However, it was not all plain sailing for Mercedes as Bottas suffered a stoppage on-track as the day's running neared its halfway point, causing the first red flag of the day due to a mechanical issue with the steering wheel on his car.

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Mercedes was not the only team to hit trouble, with Ferrari having its running limited by a problem that resigned Sebastian Vettel to the garage for most of the morning. The German nevertheless turned in a fast lap once he got back out to sit fourth-fastest behind Daniil Kvyat.

DTM driver Gary Paffett made his return to F1 machinery after four years away in Bahrain, completing 59 laps en route to fifth place for Williams. Stoffel Vandoorne was sixth for McLaren as the team got on top of the issues that limited its running on Tuesday, the Belgian racking up 49 laps.

Kevin Magnussen finished seventh for Haas ahead of Renault junior Sergey Sirotkin, while Red Bull's Pierre Gasly and Sauber's Pascal Wehrlein propped up the running order in P9 and P10.

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