With 82 trouble-free laps on the board, McLaren-Honda admit they have no idea why Day Two did not see a reoccurrence of their earlier Bahrain issues.
McLaren had a wretched weekend at the Bahrain GP with only one car starting the race.
Their troubles continued on Day One of the two-day in-season test, however, on Wednesday, the second and final day, they ran trouble-free.
As such Stoffel Vandoorne racked up 82 laps and finished fourth fastest on a 1:32.108.
But while it was a good day for McLaren-Honda, racing director Eric Boullier admits the lack of problems makes things even more complicated.
"It’s complicated to understand the issues we’ve had over the past few days, since today [Wednesday] we’ve managed to run without any problems," he said.
"Honda are working hard to understand where the weaknesses lie.
"We’ve been able to run with a more aggressive set-up today, gathered a lot of information and tested a lot of solutions, so in terms of both data and results it’s, been a very positive day of testing."
He added: "Everything has worked perfectly today in terms of reliability, and we were even able to push a little bit in terms of settings.
"We’ve managed a ‘proper’ test today, and really made the most of every opportunity out on track.
"Everything we’ve planned, we’ve tested, and we’ve done back-to-back runs, so I’m really happy with the work we’ve completed today."
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