Jerez, Spain - Renault rushed to fix a problem with its new Formula One engine on Wednesday after Red Bull's world champion Sebastian Vettel wrapped up his first pre-season test early with barely any laps completed.
While the three Renault-powered teams testing in Jerez struggled to put laps on the board, Nico Rosberg completed an impressive 97 in his Mercedes - including one unbroken 24-lap stint.
Ferrari also appeared to be making steady progress, with 2007 champion Kimi Raikkonen getting 47 laps under his belt in the new F14-T.
“Obviously we are facing problems.”
Red Bull called time on the second day with hours remaining so Renault could fix a problem with the energy store on the RB10; sister team Toro Rosso did not appear on track at all.
Renault Sport F1 track operations head Remi Taffin told a scrum of reporters crowding around his motorhome in the Jerez paddock at the end of the session: “We know what the problem is, we've got the parts to solve the problem.
“We are confident that tomorrow morning we will have all three cars on track.”
Vettel, who managed only 11 laps in total over two days, left the circuit early after a technical debrief. New team mate Daniel Ricciardo is due to be in the car for the remaining two days of the test.
“Obviously we've not had a lot of running,” Vettel admitted, “and we have a few problems to sort out, but with such big rule changes it is usual to have some teething problems.
“That's what tests are for, to sort those issues out. The next two days will be important to get some track time to prepare for the tests in Bahrain.”
Mercedes and Ferrari reported no major problems.
The teams built up useful banks of data on a day that was declared officially wet in the morning to test new Pirelli compounds but ended sunny and dry.
McLaren, which had been sidelined for all of Tuesday's first day with setup problems, ended the day fastest overall with 2009 champion Jenson Button completing 43 laps and a largely irrelevant best time of one minute 24.165 seconds.
Button told reporters at the end of the session: “There's no horrible issues with the car itself, no big issues with the power unit, in terms of how it delivers, so the basic car itself is where we want it to be.
“Something like 75 percent of the mileage done by F1 cars in the past two days has been powered by Mercedes engines, so you'd say we're in a good shape in that way if it continues like that.”
Button, now the most experienced driver in Formula One, said he was enjoying driving the car - although the noise didn’t sound as good as the old V8s - and was also encouraged by the team's ability to resolve problems quickly.
“We had a lot of issues yesterday,” he said, “and it's nice to see that we were able to solve them overnight. Not a lot of laps today, 43, but it's been a positive start.
“We did lots of different runs today. We weren't able to do any long runs because we had a few little issues but the good thing was that we were able to solve them quickly and get out there and put some laps in.”
If Button appeared subdued, despite his comparatively upbeat assessment, it was entirely understandable given the sudden death of his father John - a constant travelling companion - earlier in the month.
The driver wore helmet depicting the cartoon character 'Papa Smurf' - the nickname Button gave to his father - with 'RIP Papa' on it.
Finnish driver Valtteri Bottas, with Williams, and Mexican Sergio Perez with Force India also put on a decent amount of mileage with their Mercedes-powered cars although Perez brought out a red flag when his car stopped on track.
Marshals used fire extinguishers on the smoking car.
The only two Renault-powered cars on track managed just 19 laps between them, with Caterham's Swedish rookie Marcus Ericsson chalking up 11 - although his best time was nearly 14 seconds slower than Button.
Marussia suffered a breakdown before it had even got its car to Jerez.
The Russian-owned team had held Ferrari-engined car in its English workshop to fix problems that emerged shortly before it was due to be dispatched to southern Spain last weekend.
It finally arrived on Wednesday, in a trailer towed by a van, after a journey across the English Channel and down through France that started on Tuesday morning.
A relieved team principal John Booth said: “The van actually broke down just south of Seville - just to add to the drama!”
Marussia is the last of the 11 teams to reveal its car, although Renault-powered Lotus is not in Jerez, having failed to get its car ready in time, and has only released a computer-generated image.
The Formula One cars seen so far have been a mixed bag, with some sporting 'ugly' noses to meet new regulations and others, such as the Red Bull RB10, presenting a far more elegant front end.
Booth assured fans they would like what they saw.
“You will be amazed how pretty it is,” Booth said of his car, which he hoped would be able to get out on track on Thursday morning.
He recognised his mechanics had a long night ahead.
“The systems are so complicated, I think it took two days from finishing the car to firing it up,” he explained.
Despite the hurdles, with many more sure to come on the track, he said it was essential to be at the test.
“There is so much new stuff on the car that we haven’t even begun to understand yet,” he said.