Sepang's chaos explained: the cause, the fix and what comes next

When the Bahrain Grand Prix start procedure was suspended at Sepang after two formation laps, the immediate question was what had gone wrong with the cars.

The FIA’s review, released on Thursday ahead of the Singapore GP, now answers it, and also shows what Formula 1 will do differently from here.

What went wrong

The 2026 power units carry energy-limit restraints for wet running, and in certain sectors of the circuit a 250kW power limit was applied in wet conditions (down from the normal 350kW).

The FIA’s review found that cars running at low engine RPM in those sectors lost more power than intended, and could not recover it there.

A formation lap in the wet is a slow, cautious procession, so engines sit at low revs for longer than at any other point of a race weekend.

The mismatch between the wet-weather limits and those slow-lap conditions is what caught out a number of cars.

Several drivers, including pole-sitter Max Verstappen and second-place driver Lewis Hamilton, were affected by the issue, the Ferrari driver having to stop on the start-finish straight to restart his car before he managed to get going again.

“You know, these engines are so complicated and a lot of software is implemented,” Verstappen said after the race, which he won. “And, yeah, when there’s like some kind of… I want to call it… That’s the problem.

“I triggered it first and then I look in my mirror. I was like, ‘Wait, are they waiting for me or what’s going…?’ It was like the Lego race.”

All the cars affected by the problem were allowed to take their original positions when the race was finally started.

How quickly it was fixed

The FIA’s timeline shows how compressed the response was.

15:45: The start procedure was suspended after two formation laps.
15:50: The FIA technical team had identified the cause and released updated PU software configurations.
16:03: Teams received further technical guidance and clarifications on installing and operating the revised software.
16:20: Teams and manufacturers finished integration, with all competitors ready about 20 minutes later.
16:22: The 10-minute signal was given.
16:33: Cars left the pitlane for the start procedure.

What changes next

The race-day fix has become the baseline. The configuration established for Sepang will be reinstated for the Singapore Grand Prix if similar weather is expected.

A further wet-weather software update will follow for the United States Grand Prix on October 25.

So the patch written in the middle of a suspended grand prix will govern at least one more race, and the more considered update doesn’t arrive until Austin.

The testing question

The FIA also addressed what it called “comments” suggesting the software hadn’t been tested before it was deployed.

Its answer is that teams and manufacturers ran simulation exercises to validate the package, and that it was then run in full-scale conditions during FP1 at both the Belgian and Dutch Grands Prix.

While that was a clear rebuttal of the claim that the software went in untested, the statement doesn’t say whether they exercised the low-RPM, reduced-power scenario that failed at Sepang, as both the Spa and Zandvoort sessions took place in dry conditions.

The FIA’s own wording points to the underlying difficulty, recognising that “opportunities for testing are limited”, and it commits to strengthening PU software testing and verification through independent assessment and collaborative feedback, including input from the supplier of the standardised Electronics Control Unit (ECU).

The FIA has thanked the teams, manufacturers and its technical team for their “diligence and responsiveness”.