Ross Brawn admits that Mercedes has to work on improving the reliability of its W04 amidst uncertainty over the cause of Nico Rosberg's retirement from the Hungarian GP.
The German was forced to retire for the third time this season with an engine issue in Budapest, although Mercedes has yet to uncover the reason for the problem.
That failure was a rare one for the Brackley-based outfit, and Brawn admitted it had been one that had left the team puzzled and seeking answers.
"We're always worried about reliability, it's always very high in our list of concerns because if you don't finish a race you don't score points," he said. "It's been frustrating that we've had problems with the car and doubly frustrating I'm sure for Nico they've occurred all on his car.
"We had two chassis problems earlier in the year, we stabilised, and then we had an engine failure at the last race. That was a very unusual failure. We've not had an engine failure I think since 2008. We're investigating the recent failure. As I say, it was very unusual; we don't know what's happened."
Rosberg's three retirements – which also included DNFs in Australia and China – have cost Mercedes valuable ground in the constructors' championship, with Brawn insistent that improvements had to be made.
"Reliability is a critical thing for Formula 1 teams and we're always endeavouring to improve it, to improve the systems, to improve the quality control, improve our inspection, and improve our review process," he said.
"You just go through this loop all the time of getting to a level and then deciding how you can improve it. We're not good enough yet but the priority for the team and everybody is making a massive effort to improve it - not just trying to work harder, but work more intelligently as well."