Sometimes the lamp indicator will come on even if the all bulbs are working. The bulb fault light electronics are very sensitive and replacement bulbs from Mcparts stores (Autozone, Walmart.....) can have enough of a current draw difference to cause the car to think it has a bad bulb. Try to find an exact replacement bulb and not an equivalent.

I had this happen on the brake light on my E320. Installing an exact replacement solved the problem.

J. M. van Swaay