Sergio Perez was the pace-setter on the second day of testing at Barcelona, as gearbox issues compromise Kimi Raikkonen's running and Fernando Alonso suffers a broken exhaust... not to mention an errant rain light.

While Perez and Sebastian Vettel were around 0.5s quicker than their nearest rivals, it should be noted that both posted their best times of the soft rubber, while Hamilton posted his on hard and Raikkonen and Alonso were on medium.

Perez concluded his two-day stint by spending the morning with a series of shorter runs, aimed at gaining the engineers a better understanding of the car's track-to-wind tunnel aero correlation and its reaction to a series of mechanical set-up changes.

In the afternoon, the team ran through a number of longer runs - these were aimed at providing the Mexican with a better understanding of the methods and systems that will be used by the race team during a race weekend, including cockpit switch adjustments and understanding radio messaging.

Jenson Button kicks off his running tomorrow, his programme will pick up where Perez' left off, including further correlation and set-up work.

With poorer weather on the horizon for Friday, the team will monitor the forecast and may choose to adapt the programme in order to optimise track time over the next two days.

It was a mixed bag for Red Bull as Sebastian Vettel claimed P2 on the timesheets, but the team was forced to end its programme early when the German had to stop on track late in the afternoon.

"We had some issues with reliability today and we couldn't do as many laps as we wanted," said the German, "but I think it's better that this kind of thing happens today rather than in Australia.

"It was nothing disastrous," he continued, "just small things that hampered us today. We stopped the car once as we saw a small loss of pressure. The second stop towards the end of the day caused a red flag and it simply took too much time to turn everything around, so we couldn't get out again."

"The stops we had today weren't too serious," added Race Engineering Co-ordinator, Andy Damerum, "and we'll have everything sorted for tomorrow. We know where the issues are. However, though we would obviously much rather have had a smooth run today we still accomplished a lot and even managed to slot in some more test items in the afternoon, which we put on the car at lunch time. So, while it wasn't an ideal day, we did get through most of what we wanted to. Seb now makes way for Mark tomorrow."

A gearbox problem kept Raikkonen off track for much of the morning and part of the afternoon, and whilst the team ultimately diagnosed and rectified the issue, vital running time was lost. Once the Finn did get out on track, he immediately set the third fastest lap time, which is where he ended the day.