It happens before you even leave Singapore, not after you arrive — here's the actual rule, the actual fine, and why Causeway Kaki tracks it lane by lane.
The fuel check on Causeway Kaki's lane-by-lane view confuses first-time crossers for one simple reason: it's a Singapore rule, checked on the Singapore side, before you've gone anywhere near Malaysia. It's not a JB thing at all.
Singapore's Immigration & Checkpoints Authority requires every Singapore-registered motor vehicle to have at least three-quarters of a tank of fuel when it departs via a land checkpoint. It covers petrol, diesel (added 1 April 2019), and CNG — and for a hybrid running on both petrol and CNG, both tanks need to clear three-quarters independently.
Source: ICA's own three-quarter tank rule page (checked 2026-08-29). ICA states non-compliant drivers "will be committing an offence and may have to pay a fine, or be prosecuted in court" and may be told to make a U-turn at the checkpoint; a composition fine of up to S$500 is documented in enforcement reporting from when the rule resumed after the 2022 border reopening (Mothership, April 2022) — ICA's page itself doesn't print a figure, so treat the exact amount as "up to," not fixed.
Fuel is meaningfully cheaper across the causeway (see our own petrol-price breakdown), and without a floor on departure fuel, the cheapest way to exploit that gap would be crossing on fumes specifically to fill up on the other side. The three-quarter rule isn't new or JB-specific — it's Singapore's long-standing way of keeping that kind of round-tripping from becoming the default reason people cross at all.
ICA doesn't publish a schedule for when checks happen — they're spot enforcement, not a fixed rota, which is exactly the kind of thing a live app can track and a static page can't. What you see on the Today screen is crowd-reported: other drivers marking "Got check" or "Don't have" for the left and right lanes at Woodlands and Tuas, aggregated into a live status per lane. It's only as good as who's reporting in the last hour, the same honesty trade-off as every other live number on this app — a quiet lane isn't a guarantee, it's the best read we have right now.