Romain Grosjean confirmed that's the brake issues which plagued Haas in 2016 have still not been completely resolved.
The French driver had his first day in the team's VF-17, clocking in at 56 laps and with the eighth fastest time on the day.
"Right now we are not 100 per cent happy with the braking still," Grosjean explained.
"But we are going to work around and hopefully find some solutions early in the year."
His day at the office was a bit upset by an issue that kept the beautiful VF-17 in the team's garage but Grosjean joined the action out on the track later on.
"There were a few things that held us back in the garage so we need to work and get better in the future. But I got the first few laps in the car and learned to drive it a little bit."
Grosjean was pleasantly surprised by his 2017 charger at the outset.
"It feels pretty good. High speed [corners] are going to be interesting this year, much more than it was in the past.
" I think some of the circuits are going to be more exciting. I'm looking forward to doing more."
GALLERY: F1 drivers' wives and girlfriends
Keep up to date with all the F1 news via Facebook and Twitter
Helmut Marko believes that Red Bull and Max Verstappen are unlikely to challenge for victory…
Automotive giant General Motors is reportedly back in the game as a potential entrant in…
The opening day of running at the Las Vegas GP was a smooth but chilly…
Williams is continuing to fight uphill battles this weekend in Las Vegas as a knock-on…
It was a solid start to the Las Vegas weekend for Ferrari with Carlos Sainz…
Lando Norris didn’t hold back in his assessment of McLaren’s performance on the opening day…