Low tyre pressure light (TPMS)
One or more tyres is under-inflated, as detected by the tyre pressure monitoring system. Both rules make it yellow, and both let the same symbol also report a fault in the monitoring system itself (FMVSS 101 note 18, UN R121 note 16).
Yellow / amber
What to do
Check all four tyres with a gauge, ideally cold, and inflate them to the pressures on the car's tyre placard or in the manual. A tyre that keeps losing pressure needs inspecting. Some cars need the system reset after inflating — the manual says how.
Makes differ: what this light means on your car, the other colours it may use for the symbol and what the car wants you to do are set by the manufacturer, so your car's owner's manual is the authority.
- Symbol
- Tyre cross-section with an !
- Colour
- Yellow / amber
What the colour means
Yellow / amber — “caution”
The same colour code (Directive 2009/80/EC, Annex I, 2.1.4) gives “amber: caution”. FMVSS 101 and UN R121 write the colour as “yellow”; it is the colour both tables give to malfunction telltales such as ABS, stability control and low tyre pressure.
Where the regulations list it
| Rule | Row | Colour it sets |
|---|---|---|
| FMVSS 101 | Table 1, “Low Tire Pressure (including malfunction) (See FMVSS 138)” — telltale | yellow |
| UN R121 | Table, item 42a “Low tyre pressure (including malfunction)” — tell-tale | yellow |
FMVSS 101: Passenger cars, multipurpose passenger vehicles, trucks and buses sold in the US (S3). Table 1 gives the symbol or words and, where one is required, the colour of each telltale; Table 2 lists identifiers with no colour requirement. UN R121: Cars (category M) and light goods vehicles (N1) type-approved under the UN 1958 Agreement, which includes the EU, UK and Japan (para 1). Its table gives the symbol and colour of each tell-tale; note 2 says the symbols are substantially identical to those of ISO 2575:2004.
Good to know
- FMVSS 101 accepts the words “Low Tire”; the symbol is required only on vehicles that comply with FMVSS 138 (note 17).
Other yellow / amber lights
Sources
- eCFR — 49 CFR 571.101, Standard No. 101; Controls and displays (current text) — checked 2026-09-23
- govinfo — 49 CFR 571.101 in the Code of Federal Regulations, 1 October 2025 edition (Tables 1 and 2 as printed) — checked 2026-09-23
- EUR-Lex — UN Regulation No. 121 (01 series), Official Journal of the EU L 5, 8 January 2016: table 'Symbols, their illumination and colours' — checked 2026-09-23
- Directive 2009/80/EC, Annex I, point 2.1.4 — the tell-tale colour meanings as written into EU law (for two- and three-wheel vehicles) — checked 2026-09-23
Meanings are written in our own words from these public texts, not quoted from ISO 2575, and were checked on the date shown.