Toro Rosso has revealed that a problem with its Honda engine unit forced an early end to the final day of pre-season testing at the Circuit de Barcelona-Catalunya.
Even so, Brendon Hartley completed 156 laps for the team on Friday. He was seventh fastest after a run on the hypersoft tyres despite missing out on the final 'happy hour' runs.
In total, Toro Rosso completed 822 laps over the two-week test, its first with new engine providers Honda. That compares with just 425 laps by Honda's then-partner McLaren in last year's test.
Even more impressively, the test was completed with just one Honda power unit. That compares to McLaren being forced into making two changes of its new Renault engines this week alone.
“I’d like to thank our colleagues at Honda for a really excellent effort over the last two weeks,” said Toro Rosso technical director James Key.
"They really have only run one engine for the entirety of Test 2, and pretty much it’s run faultlessly throughout.
"[There was] a minor issue towards the end of today," he revealed on Friday. "We stopped the car as a precaution to have a look at the issue in more detail and not take any risks.
“Given we were close to the completion of our programme today anyway, we felt it was better to spend some time on that," he said. "Honda are in the process of investigating now, but otherwise everything with them has run faultlessly."
Key's counterpart at Honda, Toyoharu Tanabe, expanded on the incident that forced at early finish to the team's day.
“We used the same Power Unit throughout Test 2," he explained. "Therefore, it was disappointing that we spotted an anomaly on the data from our PU towards the end of session.
"[We] decided to stop running, as there would not have been enough time to investigate the situation fully and send the car out again."
But Tanabe didn't want to allow a minor glitch at the end of testing to cast a pall over what had been a very successful start to 2018.
“Overall, the results of winter testing have been satisfactory,” said Tanabe. "We managed to get through nearly all items on our programme, thus acquiring plenty of valuable data.
“Equally important, it was our first eight days of working at a race track together with Toro Rosso.
"Our relationship has been very open and honest and communication has been effective between all of us," he continued. "It’s only testing, but it has been an ideal start."