semiatic
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Key not detected light

On a car with keyless start, the car cannot find the key inside it. It comes on if the key leaves the car while the engine is running, or when you try to start and no key is detected. The engine keeps running, but once it is switched off it will not start again without the key.

Yellow / amber

Not defined by regulation: a maker convention

What to do

Make sure the key is actually in the car before you switch off. If the key is inside and still not detected, its battery may be flat: Kia has a separate key-battery warning that blinks amber and says to replace the battery. Your manual shows how to start the car when the key battery is weak.

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
Key with a question mark
Colour
Yellow / amber
Standard
None — a maker convention, described here from 3 makers: Volkswagen, Kia, Hyundai

Where makes differ

Volkswagen draws a key with a question mark. Kia's Key Out light blinks amber for a few seconds when the smart key is not in the car or a door is open. Hyundai uses the immobilizer indicator, which blinks for a few seconds when the smart key is not in the vehicle.

Not defined by regulation: a maker convention

Neither US FMVSS 101 (Tables 1 and 2) nor UN Regulation No. 121 lists this light, so no rule fixes its symbol or its colour. What follows is what the makers cited below say; other makes, and other model years of the same make, may draw it differently.

FMVSS 101 Table 2 and UN R121 items 35–36 define engine start and stop controls, not a key-detection lamp.

Other yellow / amber maker lights

All yellow / amber dashboard lights, regulated ones included

Sources

No regulation defines this light, so it is described from 3 carmakers' own manuals or owner pages, each fetched and checked on the date shown:

Written in our own words; the makers' pages cover their own models only.