Rear fog light indicator
The rear fog lamp is switched on. UN R121 makes this tell-tale yellow; FMVSS 101 does not list it.
Yellow / amber
What to do
Use the rear fog lamp only when visibility is seriously reduced — it is bright enough to dazzle drivers behind and can hide your brake lights — and switch it off when visibility improves. Local traffic rules set when it may be used.
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
- Lamp facing right, straight beams, wavy line
- 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 |
|---|---|---|
| UN R121 | Table, item 8 “Rear fog lamp” — tell-tale | yellow |
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
- Tell the two fog symbols apart by the beams: straight lines for the rear lamp (yellow), lines slanting down for the front lamps (green).
Other yellow / amber lights
Sources
- 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.