McLaren hit fresh trouble on day one of the second pre-season Formula 1 test, after a double electrical shutdown left Stoffel Vandoorne slowest in the morning with seven laps completed.
Following frustrations in the opening test when its mileage was dented by a wheel nut failure and a broken exhaust bracket, McLaren had hoped to hit the ground running in the second week.
But the first day got off to a bad start when the MCL33's Renault engine shut down with an electrical failure as Vandoorne returned to the pits following an installation lap.
Shortly afterwards, Vandoorne stopped out on track with the same electrical issue, bringing out the red flags and prompting a lengthy investigation at the team to work out what the problem was.
Vandoorne was able to get running again shortly before the lunch break so the team could complete a system check, but his seven-lap tally is far short of the mileage the team had hoped for.
It is understood that the electrical issue is related to the battery, but it is unclear whether the problem originates from McLaren's or Renault's side.
McLaren also appears to have been forced to make compromises to its rear bodywork in a bid to help cooling in the car, after it faced overheating headaches during the first test.
Scorch marks on the engine cover last week prompted the team to add an extra cooling slot.
As the car emerged on Tuesday, the team had added three extra slots in a bid to help hot air escape, as Giorgio Piola's exclusive photograph (above) shows.
The slots are not ideal for performance, which could mean the team is forced to tweak the design of its engine cover to help increase airflow and cooling before the first race of the season.
Gary Anderson, Technical Consultant
McLaren is pushing the limits on cooling. From the picture above we can see it has added an extra three slots to the one that it was forced to cut into the bodywork last week.
There are two brown-ish marks are on both sides of the bodywork so there is something very close to that part of the engine cover - probably the exhausts or turbo - and that is of major concern.
The exhaust temperatures on these cars runs at around 400-800C and are wrapped in heat proof insulation. If the temperature cannot be controlled, anything near them is vulnerable.
To finish first, first you have to finish - so these random reliability problems that McLaren seems to have carried over from the Honda days are of major concern, and now they have no one but themselves to point the finger at.