The second day of testing in Barcelona could have been McLaren’s best day in 2017 so far, but the team isn’t sure what’s changed.

Power unit problems have plagued McLaren since the first day of testing back in February. The team ran through four separate problems during the Bahrain GP last weekend, and an ERS water leak limited it’s testing on Tuesday.

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Honda made no modifications after Tuesday’s incident, but the team suffered no problems on the second day of testing. Great news for McLaren, but it don’t know what it’s done right.

“If we knew… this is the problem, I don’t know,” Eric Boullier said when asked. “Everything has worked perfectly.

“We are even actually pushing a little bit in terms of settings, trying to use the opportunity, and everything is working.

“This is a proper test today, everything you plan you can test it and do back to back so it’s very good.”

The reason why things went well may still be unknown, but McLaren made good use of the time on the team had.

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Boullier said the team “more or less” completed its testing programme, catching up on the track time it missed in Barcelona. Stoffel Vandoorne completed 81 laps and set the fourth fastest time of the day.

It’s good news for McLaren today, but this doesn’t mean the team can put its problems behind them.

“It is very difficult to understand what went wrong,” Boullier said. “We obviously changed the MGU-H, I think, and yesterday morning after two laps the MGU-H was gone.

“We changed the engine and did 17 laps yesterday, but we couldn’t find anything wrong physically on the car. So I think it’s going to be complicated for Honda to understand what’s wrong.

“It’s maybe coming from a batch problem, maybe some anomalies are car related… there is no common cause.”