Jenson Button is confident that there is nothing fundamentally flawed with his MP4-28 after setting the pace on Tuesday.
The Brit, who was in action on Day One at Jerez, posted a 1:18.861 to beat his nearest rival, Mark Webber, by 0.8s.
The car's debut, though, was not entirely smooth as Button did break down after just three laps in the morning with a fuel pump issue. But despite the stoppage, the 33-year-old believes his new McLaren doesn't have any problems out of the box.
"Nothing stands out as a big issue," he said. "Possibly the morning's could be but in terms of the way the car feels there's nothing that stands out as something we need to work on.
"Who knows whether it's a Championship-winning car, but the important thing is that it has a nice feeling. Lap times mean nothing right now, they don't even at the last test, but at the first race that's when you need to show how quick you are.
"The important thing is the car really does relate to the simulator. That's something that is good."
As for his blistering pace on Tuesday, Button says it doesn't count for much as he doesn't know what fuel levels and tyres his rivals were running.
"To be fair I was surprised when I saw the dash, but it doesn't mean anything.
"Some people run less fuel than others, and some people run a lot less fuel than others. Who knows? For a first day it felt good. I don't know how I did that time. Last year's car was a great car, but rules have changed. They are small, but there are changes.
"And also the tyres are different, not just in compound but in construction."