Marcus Ericsson was pleased that Sauber discovered 'no major problems' with its C34 after the first day of testing at Jerez.
Ericsson suffered a spin during the early stages after getting caught out on a cold track but returned to set the second quickest time, behind Ferrari's Sebastian Vettel.
"It was a very good day," said Ericsson, who raced for Caterham last season.
"First of all it was great to be back in the car after the winter break. I think we have good reasons to be happy. We were able to complete a lot of laps, and we went through quite a few different small tweaks on the set-up and did all the installations needed.
"There were no major problems with the car, which was really the main thing. Overall it’s been a good day, and I’m looking forward to the rest of the week. I hope we can continue like this."