bulb-out
Bulb out indicator

If this bulb is lit up, one of your other bulbs is not. Look at head and tail and indicator lights. Note this this only works if you use the correct factory specified bulbs and other bulbs (LED are notorious for this) have different physical properties and cause the system to not work properly. The right bulbs will work.








Ref: Frank Mallory's database and https://mercedes-benz-publicarchive.com