The Japanese series has a closed pitlane when safety car periods are called, and this was extended to likewise cover full-course yellows when the system was introduced for the 2021 season.
However, in last month's season opener at Okayama, both the #100 Team Kunimitsu Honda and #37 TOM'S Toyota GR Supra were caught out, pitting under FCY during worsening rain in the early stages of the race.
Both cars were hit with a one-minute stop-and-go penalty, relegating them to 12th and 13th at the finish.
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However, from this week's Golden Week race at Fuji, the exact timing of when the pitlane closes has been revised.
From now on, the pitlane will be closed from the moment the yellow flags are waved at the start of the 10-second countdown that precedes the start of the FCY 80km/h speed limit.
Previously, it was possible to pit during this 10-second countdown as the rules stated that the FCY boards being displayed marked the moment at which the pits would be closed.
It appears the change is designed to close an unintentional loophole that was created by a change in this year's sporting regulations.
Until the end of last season, the FCY boards would be displayed at the start of the 10-second countdown, with the speed limit only taking effect when the yellow flags were waved upon the conclusion of the countdown.
This was reversed for this season, with the yellow flags being waved first before the FCY boards are shown when the speed limit comes into effect.
The change was an apparent reaction to the controversy that took place at last year's Autopolis round, where two cars - the #19 Racing Project Bandoh Toyota and the #17 Real Racing Honda - escaped penalty for overtaking a GT300 car during the 10-second countdown.
SUPER GT's automatic detection system was subsequently updated to recognise when an illegal overtake was made on a car of any class, rather than just when it concerned a car passing a rival from the same class.
