Kimi Raikkonen found himself sidelined for almost three hours on Tuesday due to a problem with the cooling element of Ferrari's Kinetic Energy Recovery System.
The Scuderia, though, insist the system is progressing well, although there is still work to be done
"We're coming close to the end of this long test session here in Bahrain and the days are more and more intense," tech director Aldo Costa told Autosport following Wednesday's running.
"We have to exploit what the rules permit in terms of tests, as far as reliability, development and research in terms of performance are concerned.
"There might be some problems ahead, like the ones we've had over the two days with the completely new components of the KERS or with experiments, like the ones we had on the gearbox this morning.
"As far as the KERS is concerned I have to say that we're quite satisfied with what we've seen so far, although there's still lots of work to do.
"We used a standard configuration for the aerodynamics here in Bahrain, with just some minor updates: the complete one we'll see at the next tests in Jerez and Barcelona, where we will conclude our preparation for the Australian GP."