Last week power-unit suppliers Renault held their hands up and stated they had suffered hardware and software trouble as they attempted to get on top of the new 1.6-litre V6 turbos and ERS (energy recovery systems).

Red Bull design guru Adrian Newey further revealed this week the team had made rushed mistakes, adding the package required for cooling had also contributed to their downfall.

The hope expressed by both Red Bull and Reanult was they were on top of all the problems, and they would not materialise at the start of the second test in Bahrain.

Such hopes, however, came to nothing as the reigning four-time champions sat in their garage at the Sakhir Circuit for almost four and a half hours before finally making an appearance.

Vettel went on to complete 14 laps, only a handful of which were meaningful, before breaking down on track.

In returning to the garage on the back of a flat-bed truck, a strong smell of burning was evident, suggesting further overheating issues.

As for the other Renault-powered cars, Toro Rosso's Daniil Kvyat only managed five laps, while the debut-making Lotus completed eight.

Lotus skipped the first test due to delays in their build programme, and although they were the first car out on track in Bahrain, Romain Grosjean barely saw any time behind the wheel.

The only team seemingly able to get a grip with Renault at present are Caterham, as reserve Robin Frijns chalked up 68 laps, much to the Leafield-based marque's satisfaction.

The Dutchman's best lap was a one minute 42.534secs, finishing almost six seconds behind pacesetter Nico Hulkenberg in his Force India, who clocked a 1:36.880secs.

For anybody worried about the pace of this year's cars given the new regulations and switch from the 2.4-litre V8s to the V6 turbos, such concerns have now been allayed.

Hulkenberg's lap was a tenth of a second faster than the best posted in last year's Bahrain Grand Prix by Vettel.

Overall, Hulkenberg was 0.999secs quicker than Ferrari's Fernando Alonso, with Lewis Hamilton in his Mercedes and McLaren rookie Kevin Magnussen just off the Spaniard's pace.

Hamilton managed 74 laps and Magnussen 81 as Mercedes again suggested they have a handle on the new systems.

Ferrari also appear strong as Alonso completed 64 laps, whilst one of their customers in Sauber rattled off a day-high 82 with Adrian Sutil at the wheel.

The German was sixth on the timesheet, just behind Vettel who at least set a time of 1:40.224secs.

Behind seventh-placed Frijns came Kvyat and Grosjean, whilst Felipe Massa in his Williams and Marussia's Jules Bianchi brought up the rear with no time to their names.

Massa completed just five laps for the day due to what the team described as a fuel-system issue, whilst Bianchi's Marussia had an IT configuration problem.