McLaren's Formula One championship leader Lando Norris topped the Las Vegas Grand Prix timesheets after the second practice session was twice red-flagged due to a suspected loose drain cover.
The track action was halted on Thursday as a precautionary measure with 20 minutes to run after a marshal reported the problem just before Turn 17 of the floodlit street circuit.
Red flags were then waved again with just over two minutes remaining to end the session shortly after the drivers had returned to the track following a 15-minute delay.
Governing body FIA said on-site personnel had reported the same manhole cover was still shifting as cars passed over it and the situation was checked as a precaution.
FIA said in a statement it had inspected and welded down loose manhole covers.
"The manhole that prompted the red flag in FP2 was disassembled and further inspected. A specific fault was found with the closure mechanism, and it was possible to address this issue overnight.
"In addition to the work conducted to address the issue identified, the cover of this manhole has been welded to provide further mitigation.
"All other manhole covers on or close to the racing line were reinspected overnight, and additional welding was applied to a further 14 manhole assemblies."
Loose drain covers were a problem in practice for the inaugural Las Vegas Grand Prix in 2023, with one wrecking Carlos Sainz's Ferrari when he drove over it.
Norris, who has a 24-point lead over teammate Oscar Piastri going into the race with three rounds remaining, produced a best time of 1:33.602 seconds on the soft tyres after Ferrari's Charles Leclerc set the pace in practice one with 1:34.802.
"We didn't manage to get too much from FP2, given the disruption, but we did get a slightly better feeling than in FP1," Norris said, referring to the two practices.
"We made some good progress and we've got a reasonable feeling altogether. Some positives to build on and some areas to try and improve going into tomorrow."
Norris had brushed the wall without damage in that opening session and was sixth, while Piastri was eighth.
The Australian was 14th in the second practice after having to abort a quick lap before the first red flag, and not getting in a lap on the softs, with McLaren looking more competitive on the evolving track.
Mercedes' Kimi Antonelli was second, 0.029 slower than Norris, and Leclerc third, the Monegasque stopping with four minutes remaining.
New Zealand driver Liam Lawson performed strongly in his second visit to the Las Vegas circuit, on a track again made slippery in parts by rain.
His best time was 0.299 seconds slower than Norris ahead of a third practice session and qualifying on Saturday afternoon (NZ time).
"It was ok," Lawson said.
"We struggled a little bit in P1 today. In P2, not everyone got their laps in.
"We're not quite as good as we look, but I think we're in a better place than when we started today - that's the main thing."
- RNZ and Reuters
