Fabian Coulthard, who led for the first stint of the 78-lap race, was running a strong second when he felt the car's brake pedal start to give. The team monitored the situation for several laps but decided to bring him in after he slipped back to fifth.
Some quick repairs saw Coulthard re-join 19th but a lap down, where he finished.
Coulthard is now looking forward to tomorrow's qualifying at 11.05am, saying the car is as good as any out there.
Fabian Coulthard Lockwood Racing "It's a credit to the guys that we could run at the front for so long but unfortunately when you start at the front and race at the front you want to finish at the front. The cars are fast and as good as the other cars around us if not better so there are plenty of positives to take away.
"With the problem I had, you push the pedal and it goes to the floor; it's quite a fundamental issue around here! I did a few slow laps to see if I could circulate to the end but it just became dangerous.
"The problem is solved now. We came in and bled the brakes and it was like normal. There was a slow leak but the guys will be onto it tonight and we'll be back again tomorrow. There's no reason why it should happen again."