The FIA moved to ban an MGU-K shutdown and SECU software trick used in qualifying by Mercedes and Red Bull-powered teams, closing a power-unit loophole that gave short tactical boosts.

Teams had been using an emergency SECU override to shut down the MGU-K and retain maximum electrical deployment to the line, sidestepping the mandated 50 kW per second ramp down and generating brief 50–100 kW power bursts that yielded qualifying advantages measured in hundredths of a second.

Rival teams first flagged the behavior after the season opener in Australia, and the tactic was observed again at Suzuka in Japan.

Sources