Sepang formation lap stoppages traced to bug in FIA wet-weather software

The Bahrain Grand Prix at Sepang on 4 October saw its first start attempt abandoned after a number of cars lost power on the formation lap. The cause was not the teams but a wet-weather setting in the FIA software that runs on every car. The FIA distributed a fix to all teams during the rain delay, and the race eventually got under way from the original grid order.

What happened on the formation lap

Max Verstappen, Lewis Hamilton and several others were unable to accelerate on the formation lap, with cars crawling or coming to a halt. Hamilton said he had to stop on track, switch the car and engine off and restart it, something he had never done before (Road & Track). Oliver Bearman said his throttle pedal stopped working and that the engine was just idling as if it were not connected, while Sergio Pérez called what happened totally unacceptable for the sport (Road & Track). MotorBiscuit reported that Esteban Ocon also stopped at the side of the track.

The start attempt was called off, and with no team at fault and no regulation covering the scenario, the FIA kept the original starting order (MotorBiscuit, Sky Sports). Reports of the delay vary: The Race put it at more than 45 minutes, Sky Sports at around an hour for the fix, and Grande Prêmio at more than 90 minutes including the rain.

Turn 9 at the Sepang International Circuit, one of the sectors where wet-weather mode caps MGU-K output at 250kW (The Race). Map: Pitlane02, Wikimedia Commons, CC BY-SA 3.0.

How the bug was triggered

In its statement the FIA said an unprecedented combination of low engine speed, low-grip conditions, wet-weather energy management settings and the Sepang circuit's sector configuration led to an unintended loss of power for a number of cars (GPFans, Sky Sports). The 2026 power units take almost half their output from electrical power and have no MGU-H (Sky Sports).

According to The Race, in the wet the FIA software caps the electric motor (MGU-K) at 250kW instead of the 350kW available in the dry, because of safety concerns over the high torque. The reduction is imposed in certain sectors, and the Turn 9 left-hander at Sepang is one of them. As cars ran extremely slowly, boost pressure fell and the MGU-K could not make up for it. That triggered a 60-second protective lockout designed to stop teams deliberately shutting down the MGU-K, and it could also cut combustion engine power. FIA single-seater director Nikolas Tombazis described it as a loop that meant the cars could not reaccelerate, and stressed it had not been the teams' fault (Road & Track, GPFans).

A fix built in 20 minutes

The FIA Technical Department removed the energy limit in the affected sectors through a software release distributed to all competitors during the rain delay, allowing teams to change their power unit settings before the start (FIA statement). Mercedes deputy team principal Bradley Lord said all the teams had been sent new parameters to load into the cars (GPFans). Installing and checking the update took about 20 minutes (The Race, MotorBiscuit), and Tombazis admitted it was a bit of a rush job but said it did not compromise safety or fairness (Road & Track).

Why it was not caught earlier

The FIA acknowledged that neither it nor the teams had detected the issue during testing or on the laps to the grid. Tombazis said the software had not been tested as extensively as the FIA would have liked because there had been very little wet running this year (The Race). The Race noted this was the first proper rain running for the 2026 cars in an official weekend session, and that the only earlier wet running, Pirelli's tests at Suzuka and Ferrari's artificially soaked Fiorano in April, did not reproduce slow-speed conditions like those at Sepang.

The FIA will carry out a full review with the teams and power unit manufacturers. Asked whether it could happen again, Tombazis replied that he could guarantee this specific problem would not, but not that no problem would (The Race).

What happened on the formation lap

How the bug was triggered

A fix built in 20 minutes

Why it was not caught earlier

Sources