Lewis Hamilton fastest in Malaysian GP second practice
Mercedes' world champion Lewis Hamilton set the fastest time in second practice despite a session punctuated by technical problems.
Hamilton missed the first session and the start of the second with an engine problem but was still 0.373 seconds clear of Ferrari's Kimi Raikkonen.
His team-mate Nico Rosberg was third fastest after failing to get a clean run on the fastest tyres.
The McLarens of Fernando Alonso and Jenson Button were 16th and 17th.
Alonso is taking part in his first race weekend of the year after missing the Australian Grand Prix two weeks ago on medical advice because of concussion suffered in a pre-season testing crash.
Hamilton's pace-setting time was immensely impressive in the light of a series of problems with the car.
The world champion suffered an engine problem in the first session before setting a lap time and was told to switch off and park out on track because the team had no telemetry, which can help inform the team how much damage might be done by continuing to run.
He missed the first part of the second session while Mercedes completed repairs but was called in again after just five laps because the team again lost all telemetry.
In a difficult session for Mercedes, Rosberg failed to get a clean run while simulating qualifying on the medium tyres and ended up 0.055secs slower than Raikkonen.
|Andrew Benson on Sepang's extreme temperature|
|"Malaysia's tropical heat and humidity are in full swing.|
|Despite the strong wind on Friday, walking around Sepang in these temperatures is like being in a damp oven.|
|What it must be like for the drivers, wearing four-layer fireproof overalls, fireproof underwear, a helmet and balaclava, in cockpits where temperatures will top 60C does not bear thinking about."|
But BBC F1 analyst Allan McNish said the long-run times set during the race simulations in the final part of the session suggested Mercedes still had an advantage of between 0.7secs and a second over Ferrari.
McNish said: "Ferrari are the best of the rest but the gap to Mercedes is exactly the same as it was two weeks ago in Australia.
"Lewis Hamilton, despite all his problems, was able to bang in a lap time and it shows their dominant form."
Vettel would almost certainly have been in the top three overall if he had not had his first lap on the mediums wrecked when the session was stopped because Manor's Roberto Merhi was beached in a gravel trap at Turn 11.
The German then spun on his second attempt, at the same place as Merhi.
There was encouragement for Red Bull after a difficult first race. Daniil Kvyat was an impressive fourth fastest overall, ahead of the Williams cars of Valtteri Bottas and Felipe Massa, but his race-simulation run was truncated when he hit trouble with his engine.
However, it is likely Kvyat's pace was flattered by the Russian doing his run later than others, when there would have been more grip on the track.
Team-mate Daniel Ricciardo was down in 10th place after managing only six laps.
Toro Rosso's Max Verstappen was eighth fastest, ahead of Sauber's Marcus Ericsson.
Lotus also had a troubled session. Pastor Maldonado, who ended up 11th fastest, saw his rear bodywork come loose on the straight and team-mate Romain Grosjean was 18th fastest after hitting engine trouble midway through the session.