Concerns about the reliability of its new MGU-K in pre-season testing led it to adopt a no-risk strategy in the opening races by reverting to last year's specification.

It was not ideal for the works outfit and customers Red Bull and Toro Rosso given the older spec is 5kg heavier and requires an extra 1kg air bottle for cooling.

But after investigations at Renault's engine base at Viry, the French manufacturer has brought a revised version to run during the two-day test in Bahrain, starting Tuesday.

Renault F1 managing director Cyril Abiteboul told Motorsport.com the works team will run it in Bahrain but "it is up to the customer teams to decide" if they do so.

He added: "According to all the tests this week, [its introduction] could be for Sochi. The MGU-K can be back on track fairly quickly.

"It will help a little bit with the weight and with the packaging, so for all these things it's good to have it back. It will also be good to have back a complete 2017 configuration.

"It helps bring confidence our ability to bring performance, upgrades to the car and the engine."

Abiteboul said Renault's main concern was reliability and only once that is sorted will it turn its attention to performance and the introduction of a new engine spec.

The timing of introducing new specifications is even more crucial this year as teams are restricted to just four units without penalty for the 20-race season.

"The engine plan is challenging because of the reliability situation - that is not where we want it to be," he said. "As soon as reliability is under control, I'm confident we can bring more, more from fuel, more from oil.

"There are lots of areas where we have progress to come."

When asked if there was a plan to introduce a new engine spec at Barcelona, Abiteboul said that was the target or at least before the summer at race seven or eight, which would be Canada or Azerbaijan.

"That is the sort of thing we're still working towards," he said. "Definitely an upgrade before the summer, race seven, race eight. One thing that is so important is to be in sync with the engine allocation plan.

"As soon as we have a reliability issue, it means you need to bring forward the engine introduction. That is the sort of thing we need to observe and monitor to honour that plan."

Renault scored its first points of the season when Nico Hulkenberg finished ninth in Bahrain.

Additional reporting by Ben Anderson