LONDON Red Bull and Renault will be working flat out to ensure Formula One championship leader Sebastian Vettel does not go into next weekend's title showdown in Brazil with a 'ticking time bomb' deep inside his car.
Vettel leads Ferrari's Fernando Alonso by 13 points ahead of the final round at Interlagos after finishing runner-up to McLaren's Lewis Hamilton in Sunday's U.S. Grand Prix in Austin, Texas.
While Red Bull clinched their third constructors' title in a row, the celebrations were muted by Vettel being denied his third successive crown for at least another week and reliability problems affecting Australian team mate Mark Webber.
"Reliability is a concern, it's unfortunately our third alternator failure this year which is a ticking time bomb," Red Bull's technical head Adrian Newey told Britain's Sky television.
"You never know when that one is going to strike. Renault haven't managed to find a proper solution to that one so that's a continual worry in the back of our minds as is the rest of the reliability.
"The cars are very complicated and keeping them going around is anything but guaranteed."
Webber pulled over after his car's alternator failed, a recurring problem for the Renault-powered team this season, while he was running in third place at the Circuit of the Americas.
A similar failure halted Vettel at the European Grand Prix in Valencia while he was leading and the 25-year-old German also suffered alternator problems at Monza in Italy when he stopped six laps from the end.
Other Renault-powered teams have had reliability problems and the manufacturer made new specification alternators available for the race in Austin.
With so much at stake, Red Bull stuck with the type they had used since Monza without trouble only for Webber to pay the price.
"We had low battery voltage for a few laps before and then I lost gearbox sync and KERS, something was happening on the battery side," said the Australian.
Team principal Christian Horner hoped they would have the new version for Brazil and Vettel was confident his team would resolve the issue.
"I think we've managed the last couple of races pretty well so I'm sure it should be easy to explain, to find the problem," said the driver after the race.
"After Monza, I think we learned the lesson and we should be prepared enough for next week."
Alonso, who finished third on Sunday in a Ferrari that has been one of the most reliable cars on the grid, recognised Red Bull's weak spot and was hopeful that it might be Vettel's turn to be vulnerable in Brazil.
"We saw today again that Webber retired, sometimes it is the alternator, sometimes it's the KERS, sometimes it's the brakes. It always happens to that car so maybe in Brazil it changes cars," said the Spaniard.
Vettel will win the title in Brazil if he finishes fourth or higher, regardless of what Alonso does.
(Reporting by Alan Baldwin, editing by Justin Palmer)