Renault's head of track operations Remi Taffin has admitted that the French engine supplier is facing problems, but is hopeful that the situation will improve for the final two days of the Jerez test.
Renault powered cars managed just 19 laps on Wednesday, with Red Bull, Toro Rosso and Caterham all restricted by a suspected battery problem.
Sebastian Vettel managed only eighth laps with Marcus Ericsson completing 11 laps before his car ground to a halt. Daniil Kvyat did not make it out onto track all day.
By comparison, Ferrari powered car managed 100 laps while Mercedes amassed over 200 laps at Jerez.
"The fact is that we are facing problems [as] there are many problems when you have new cars," said Taffin.
"For sure, we know on our side we had one problem which we clearly identified and we wanted to fix it. We could not fix it so we did as much as we can on our side to make sure for tomorrow, especially for Red Bull and Toro Rosso that we can take to the track at nine o’clock."
"Hopefully we can have all three cars on track [tomorrow morning]."
Taffin said that the complexity of the new power units was exacerbating Renault's issues.
"You have to bear in mind that the power unit is made of different components."
"It's not that any one of them is not working, it’s a problem of integration and with this problem we had to fix the energy store but I'm not going to go into detail on the problem. We have the parts, we have the people here to do this and are prepared to do this," he said of fixing the problems.