Vettel leads Ferrari's Fernando Alonso by 13 points ahead of the final round at Interlagos having finished second to Lewis Hamilton in Sunday's US Grand Prix.
While Red Bull clinched a third constructors' title in a row, the celebrations were muted as Vettel was denied his third successive crown for at least another week and reliability problems affected Australian team-mate Mark Webber.
"Reliability is a concern. It's our third alternator failure this year which is a ticking time bomb," said Red Bull's technical head Adrian Newey.
"Renault haven't found a solution so that's a continual worry as is the rest of the reliability. The cars are complicated and keeping them going is anything but guaranteed."
Meanwhile, Hamilton believes he can now leave McLaren after achieving his "ultimate high" regardless of what unfolds in Brazil on Sunday.
The victory Hamilton has craved since announcing his departure at the end of September on a £45million, three-year contract with Mercedes finallycame his way in Texas on Sunday.
He said: "It would be nice to be battling for the championship, but that's not the way it is.
"But I believe I showed I have the status and drive the others do, even though I'm not competing for the championship.
"I've been driving my best all year, and I've been getting stronger throughout, and for me this is my strongest race of the year.
"To hunt Vettel down and see him mistakes whilst applying the pressure was a great feeling."
