Barcelona: Romain Grosjean marked Lotus' return to the track with the fastest time on Thursday on the opening day of the final testing session before the new Formula One season starts.
After fixing a chassis problem that forced Lotus to pull out of last week's practice, also at Catalunya Circuit, the French driver waited until near the end of the afternoon session to clock a day's best lap of 1 minute, 23.252 seconds.
Grosjean will drive again on Friday before Kimi Raikkonen takes the wheel for Lotus on the final two days of testing.
McLaren driver Jenson Button was the second fastest, 0.258 seconds back.
"Having completed more than 2,000 kilometers at Barcelona last week, today was always going to be more about quality than quantity," McLaren team manager David Redding said. "We wanted to drill a little deeper into our understanding of the car, and that meant undertaking some bigger set-up changes that wouldn't ordinarily be available to us during a grand prix weekend."
Mexican driver Sergio Perez of Sauber was next, 0.568 seconds off the pace.
"I think this was a very good day for me. The car was performing well under varying conditions," Perez said. "We are working in the right direction, and I'm very much looking forward to getting into the car again for my final day of testing on Saturday."
Red Bull's Mark Webber was fourth, followed by Nico Rosberg of Mercedes, who completed the most laps with 128 under a sunny sky.
"We certainly have a few more boxes to tick," Webber said. "We have some crucial data to gather this week and the next three days will be really important. We're learning every run and we are making progress I think."
Ferrari's Felipe Massa finished with the eighth fastest time of the 10 teams running.
World champion Sebastian Vettel will drive for Red Bull on Friday, along with Ferrari's Fernando Alonso and Lewis Hamilton of McLaren.
The season opens at the Australian Grand Prix in Melbourne on March 18.