Romain Grosjean said he was relieved Haas has managed to cure the brake-by-wire problems that limited the Formula 1 newcomer's running in testing.
The Frenchman caused three flags over the course of Thursday's running at Barcelona, twice ending up in the gravel, because of a BBW issue.
But after working late into the night, Haas found a solution and Grosjean had a successful morning on the final day, logging 53 laps.
Grosjean said: "The solution is much better, a safer and more competitive solution.
"It felt much better, it was a good relief for everyone.
"If you don't have the brakes, then it is very hard to drive the car.
"The guys worked hard, all night long to solve the issue.
"There is still a lot of work we need to do but generally everyone did an amazing job.
"It was a very good morning."
Grosjean said he stuck around in the garage, working on his seat while the mechanics worked to fix the problem.
"I was fine-tuning my seat at the back of the garage," he said.
"It's important to help the guys, everyone is tired switching between day and night shifts.
"The way everyone has worked and reacted to problems has been impressive. The morale has never been down.
"It's been tough for everyone, especially for the guys who have been away from home for one month.
"They have done an amazing job, they have been on it all the time. For a new team, we impressed everyone."