Disqualified from the session after scrutineers could not extract the necessary litre of fuel for sampling, the championship leader had been asked to stop the car urgently following advice from engine supplier Renault.
It emerges that Renault feared damage to the engine and other systems if Vettel's RB8 had been left to run completely out of fuel.
"We saw some numbers going down," said Vettel, "and in order to save the engine, save the pumps in between etcetera, we decided to stop the car, convinced that we had enough fuel in the car to provide a sample."
So why wasn't enough fuel put in the car for the decisive qualifying session?
"It's difficult," team boss Christian Horner is quoted by Germany's RTL, "because Renault was sure there was enough fuel in the car.
"What happens is the engineers for the engine side calculate the amount of fuel to be put into the car. As a team, we (Red Bull) are not involved in it," he insisted.