Renault's technical deputy managing director Rob White has conceded that the French's company's performance at the Jerez test was not acceptable.
The three teams powered by Renault at Jerez managed just 151 laps, compared to the 444 completed by rivals Ferrari and 875 by Mercedes powered outfits.
Renault's cars were also significantly off the pace, with Jean-Eric Vergne's time of 1.29.915s being their fastest time of the week, some 6.6s slower than Thursday pacesetter Kevin Magnussen.
"We have not run enough laps, and when we have they have not been run at an acceptable performance level," said White.
"The underlying causes are not straightforward: there isn’t a single component or system that has caused particular trouble."
"A number of related things have been troublesome, principally concerning the control and operation of the various sub-systems of the Power Unit within the car."
"On the first run day, we had problems with a sub-system within the Energy Store that did not directly concern either the battery nor the operation of the battery – it is an electronic part that was in the same housing as the Energy Store."
"We subsequently had problems with turbocharger and boost control systems with knock-on effects on the associated engine management systems, subsequently provoking mechanical failures."
White believes that Renault now understands the problems that they encountered at Jerez.
"Several problems are common to all [teams], as the power unit is the same specification in all the cars except for relatively minor installations differences. Some problems are particular to one installation environment, but it is our responsibility to deal with all of them."
"In general, the individual issues are understood; we have worked with all three teams running this week and despite appearances, have made some useful progress. We have not uncovered any big new fundamental problem, although we must recognize that our limited running makes it impossible to be certain."
White is adamant Renault will have a solution for the next test, which takes begins in Bahrain on 19th February.
"We recognise that when the cars have run, they are not running at an acceptable level."
"We are a long way from the type of operation we had planned and prepared for – largely as a result of the workarounds we have implemented – but all the information is useful."
"In dealing with the issues we have moved further away from the configuration we were comfortable with, which has resulted in the relatively slow times, but the running has given us a vastly greater understanding of the issues we face. We absolutely expect to have a more definitive solution in place for the next session in Bahrain."
"It is unacceptable that we have not been able to mitigate the problems sufficiently to allow our partners to run at any length. We are working hard to correct this in time for Bahrain and aim to make amends there."