The three Renault-powered cars that appeared in the first four-day test in Spain managed just 151 laps between them and intense work has been underway to fix the problems ahead of the first Bahrain test, which kicks off on Wednesday.
Renault has completed promotional running days with Lotus at Jerez and Scuderia Toro Rosso at Misano, with head of track operations Remi Taffin optimistic about progress.
"Mainly, we were facing hardware issues, and consequently also software issues," said Taffin.
"The first one we pointed out was the energy store problem. We had good upgrades that we could test either on the dyno or on track as we had two filming days and everything worked as expected.
"So we are now confident that the problem we had in the first test are now solved when we look into the hardware and especially the energy store.
"The next chapter was obviously software. In the first test, we had some poor driveability on track that was mainly traced to either boost control and calibration issues which we have taken on for the last two weeks on the dyno and we have improved our level.
"We are now still a bit behind our initial schedule but we now have done what we would normally have done in the first test. So we should be OK in Bahrain.
"The last point was the integration issues we could have faced with our customers.
"We have worked on the dyno with them and we will get into Bahrain and the first day without all of the issues that we had in the first test, which we now believe are closed.
"We are ready to go into what we would have liked to do in the first test, which is testing properly the power unit and trying to give our customers the means to 'discover' their cars."
Problems with Toro Rosso
While the second of Lotus's two days of promotional running ran smoothly, with the team racking up the maximum permitted 100kms, things did not go so well for Toro Rosso.
Taffin admitted that Renault had hoped to get away with some minor issues that had not held back Lotus, but that this was not the case.
"We hoped not to have any problems, but we had a few further ones," said Taffin.
"But in fairness, it was not a surprise. We knew what we had in the car and we thought we would get away with it based on what we did in the first filming day [with Lotus], but obviously not.
"The reasons are well-known on our side and we have since worked on it but there is nothing we can do on a filming day.
"When you start the day off with a configuration, you have to run all through the day so it's difficult to react."
Catching up, but still behind
Taffin accepted that Renault is still on the back foot, but laughed off suggestions that it is months behind its rivals in terms of engine development.
"We are still behind schedule, but it's not a question of months," said Taffin.
"I think we are at least where we would have thought to be for the first test so maybe we are now three weeks behind and we are on a plan to recover.
"We are now going to go into Bahrain with what we would like to have finished the first test with."