Esteban Gutierrez says Sauber's progress with its 2014 car is being hampered by problems with its braking system.

The new brake-by-wire system introduced for 2014 - which sees brake balance being electronically adjusted to compensate for the energy recovery systems during their harvesting phase - has proven troublesome for Sauber so far, with Adrian Sutil spinning on numerous occasions during pre-season testing.

Speaking about the problems during the second test in Bahrain, Gutierrez told reporters including Crash.net that both he and Sutil are struggling to improve the car balance while the braking issues persist.

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"As a driver it's all based on the feeling because obviously you need to communicate with the team what you feel and what you need to be more confident and to get more performance from the car," Gutierrez said. "This is affecting the car balance as well so you need to relate everything to speak about the car balance. You can't just speak purely about the car balance; when you have all these issues on the braking you need to solve the braking issues and then go on to the next step."

And Gutierrez said the problems are being treated as a priority by Sauber as the start of the new season draws closer.

"It's more complex because you have a system which is working and trying to compensate for something from the recovery system and it has torque variations as well to make in relation to the downshifts. So this is something that we need to put together and make progressive.

"We are making progress but we have this as a priority at the moment."