Engine suppliers Renault apologised to Formula One champions Red Bull at the Italian Grand Prix on Sunday after the team failed to score a point in a race for the first time since 2010.
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Double world champion Sebastian Vettel rolled to a halt with what was diagnosed as an alternator failure - the same problem that denied the German a victory in Valencia in June when he started on pole.
Australian Mark Webber retired after inflicting too much damage on his tyres to continue safely. The last time Red Bull drew such a blank was in South Korea in October 2010.
"We changed the alternator on Sebastian's car yesterday, but unfortunately we had the same failure in today's race," said Renault engineer Cyril Dumont.
"We are still looking into why this happened, but we do know that even though the alternator was being operated entirely within the prescribed range, the part itself overheated and shut off the power supply.
"We have to apologise to Red Bull Racing as clearly this has hurt us in the Championship. We have no option but to sort it out, and it will still be a priority before Singapore," he added.
Vettel, now fourth in the championship and 39 points off the lead after starting the day second, said he knew he had a problem about 300 metres before the car stopped when his pit wall told him to pull over immediately to save the engine.
He had by then already collected a drive-through penalty for forcing Ferrari's championship onto the grass and gravel at 330kph.
Team principal Christian Horner said the two failures had been extremely costly, even if Red Bull still led the constructors' standings by 29 points from McLaren, with seven races remaining.
"Very disappointing but we need to work with Renault to try and understand it and make sure it doesn't happen again," he told reporters.
"Sebastian did nothing wrong. He drove as hard as he could and this circuit unfortunately exposes our weakness."
