Manama, Bahrain: Four-time world champion Sebastian Vettel admitted Red Bull were facing serious problems after he failed to complete a lap in testing on Saturday, just two weeks out from the start of the new season.
Vettel's car suffered electrical issues which meant he stopped on the installation lap at Sakhir and then spent the rest of the day frustratingly kicking his heels in the garage.
The setback came just a day after teammate Daniel Ricciardo had completed 66 laps in the second Red Bull for the Australian's most convincing outing this winter.
"At the moment we obviously have lots of different problems we are curing," said Vettel, who will have his final test run of the close-season on Sunday before the season gets under way in Melbourne on March 16.
"It's not the best situation to be in but we can't change it. Obviously reliability is still a big question mark. It's difficult to say how long it will take to remedy. I think some things will just come down to the fact that in two weeks' time we'll have lots of new parts on the car.
"We've had some damage because of the problems we've had here and the parts aren't available overnight, so from that side I think things will get better over the next couple of weeks."
Williams driver Felipe Massa topped the time charts with a time of 1min 33.258sec off 99 laps with Mercedes driver Nico Rosberg in second spot just ahead of Ferrari's Kimi Raikkonen.
"We had a very good day today doing almost 100 laps. We did a lot more performance work in the car which is something that we haven't done so much of so far," said Massa.
"I'm really happy with the car and feel we found a good balance. We did so much work on the set-up but it is very important that we go to Australia prepared."
Times on the third and penultimate day of pre-season Formula One testing at Bahrain's Sakhir circuit on Saturday:
1. Felipe Massa (BRA/Williams) 1:33.258 (99 laps), 2. Nico Rosberg (GER/Mercedes) 1:33.484 (103), 3. Kimi Raikkonen (FIN/Ferrari) 1:35.426 (87), 4. Kevin Magnussen (DEN/McLaren) 1:35.894 (88), 5. Daniil Kvyat (RUS/Toro Rosso) 1:36.113 (81), 6. Nico Hulkenberg (GER/Force India) 1:36.205 (115), 7. Jules Bianchi (FRA/Marussia) 1:37.087 (78), 8. Marcus Ericsson (SWE/Caterham) 1:38.083 (117), 9. Romain Grosjean (FRA/Lotus) 1:42.166 (33)
No times: Adrian Sutil (GER/Sauber) 1 lap, Sebastian Vettel (GER/Red Bull-Renault)