Haas' programme on the opening day of testing in Bahrain suffered a minor setback due to a technical issue encountered by the team with its Ferrari power unit.
Ferrari has worked hard since last year to improve the reliability of its engine – a weakness that proved costly last season.
F1's engine regulations have frozen the specifications of each manufacturer's power unit until the end of 2025, but development work focused on reliability is authorized.
While the Ferrari team had no problems during the day, Haas did report an issue with their power-unit that cost them track time.
Haas team principal Guenther Steiner said the team's mechanics had to disassemble a large part of the rear bodywork on the VF-23 to fix the issue.
"You have to take everything off to get to it and then fix that," he explained. "We didn’t lose a lot of time, but I mean, if you have nine and a half hours a day, to lose an hour or two, that’s a lot of time percentage wise."
Despite the hold-up, drivers Nico Hulkenberg and Kevin Magnussen still racked up 108 laps between them, compared to 136 for Sainz and Leclerc.
"We didn’t lose a lot to be honest. One run with tyres," shrugged Steiner, who was confident that the issue had been addressed and wouldn't recur.
"We still need to find out where the car is and get the best out of it, but otherwise, pretty happy," he said.
Ayao Komatsu, Haas' director of engineering, confirmed that the team did not fully complete its run programme on Thursday. But the Japanese engineer nevertheless had a good feeling based on what was achieved.
"The objective of the first day of pre-season testing was to understand the fundamentals of the car – ride-height, stiffness, balance in the right window and mileage and reliability – so we tried to do as many laps as possible," he said.
"We didn’t 100 percent meet our objectives, but Nico did 51 laps in the morning and Kevin did 57 laps in the afternoon, which is pretty good.
"We only had minor issues, but we understand the solution.
"It’s too early to talk about performance but our initial feeling is good from what we achieved – so it’s a good start for day one."
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