Mark Webber was left frustrated by his lack of running in second practice for the Abu Dhabi Grand Prix after being hit by car problems again.
The Australian, who had endured a difficult race in India after having issues with his KERS, managed only 21 laps in the second session after his mechanics had to work on his car, which was leaking some fluid.
The Red Bull driver admitted he was not sure yet about the cause of the problem.
"It looks like [a] water generator or some KERS issue, it was a pain," said Webber, fourth fastest in the session.
"It's not great when any running is limited, you always want to get as much as you can in.
"That is it today and we come back tomorrow.
"The track moves around a little bit but not too much, [but] it is never a help to have less running.
"We have tonight to fix it and come back tomorrow. We will look through stuff tonight. I have no idea what happened on long runs but tyres don't look too bad."
Team-mate Sebastian Vettel did not encounter such problems on his way to the fastest time of the day, although the championship leader said there was still work to do.
"We need to work on the car overnight, but the pace was not bad," he said. "It was quite slippery today with all the drivers. We saw that many cars were off track here as they are trying to explore the limits.
"That is what we usually do on a Friday, we are more or less there, but we need to make sure we get the car forward."
Vettel, who topped the session ahead of McLaren's Lewis Hamilton, believes the Briton may be his main rival this weekend.
"It looks like [that]," Vettel said.
"At least today the battle was on with him, he was very quick on the medium tyre so we need to do a little bit of catching up to make sure we are very close to them and possibly ahead of them tomorrow."
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