"There's a few things we needed to tighten up on our side but nothing major and obviously Renault have some issues that they are tidying up as well," team boss Horner told Sky Sports News.
"But these cars are so complicated that even small problems can cause big failures."
But despite suggesting the problems with the RB10 are minor, Horner was also giving no guarantees they will all be fixed by next week, when the second official test begins in Bahrain.
"Obviously there's quite a bit to do but there's still a fair bit of time before the first race," he said.
"Bahrain is an important test and we are working very hard at both Renault and Milton Keynes.
"We don't want another test like Jerez but that's what testing is for -- you sort your problems out so as not to have them at the races," Horner added.