Lewis Hamilton has set the fastest lap time on the final day of testing at Bahrain, after completing 70 laps of the circuit.
His Mercedes-Benz, which took lead position with a 1m33.278s lap, was the quickest out of a total of 12 cars undergoing testing.
Despite suffering a gearbox problem in the morning, he successfully returned to the track to secure the top position.
Problems with the dramatically different 2014-season cars are still rife, however, and Lotus, McLaren and Force India all experienced engine failures.
Red Bull suffered from further issues too, with a technical issue causing driver Sebastian Vettel to lose control at the end of the morning's session. Kamui Kobayashi also had problems, with a damaged clutch bringing his car to a stop.
Williams' Valtteri Bottas set the second-fastest time of the day, a lap of 1m33.987s, followed by Ferrari's Fernando Alonso at 1m34.280s.
Previously, Felipe Massa had set the fastest time on the penultimate day of pre-season Formula 1 testing in Bahrain.
The Williams driver set the pace during the morning session, eventually putting in a best time of 1m33.258s over 99 laps. The day was again overshadowed, however, by the continued woes of world champion team Red Bull.
Sebastian Vettel broke down halfway into his installation lap, and, upon his recovery to the pitlane, Red Bull erected screens in front of their garage to keep prying eyes away as they seeked to resolve their latest issues. Both Sauber and Lotus also suffered technical problems today.