Our first idea from decades of life experience with refrigerators was that some light bulb needed changing. After thorough inspection, however, no conventional light bulbs were to be found. Under the ceiling cover, we found two tiny LED lights that we first did not recognize as light sources at all and do not look like they should be removed. There is no easy way to open the cover of the back illumination either. The back is lit by a Laser light source. The manual recommends to call a service technician. Welcome to German precision goods in the 21st century! No way for less-talented rocket scientists to even change a light bulb!
But before we extend a time-consuming and costly invitation to Herr Dipl. Ing. Bosch's faithful associates, here is a remedy easy enough for us to try. When we open the door to the refrigerator compartment, we see two push button switches at the top of the refrigerator's frame. The left one is a small rod that is pushed in by the door when we close it. The right switch shows a reboot symbol adopted from the PC world. That switch represents the on/off switch for the whole refrigerator. When we pushed it, the lighting in the compartment - ceiling and back - sprang to life briefly, before the refrigerator shut down and the display above the water and ice dispenser fell dark. We pushed the switch again to restart the refrigerator.
The short resurrection of the compartment lighting during shutdown suggested that the light sources were actually still intact, but were not switched properly.
The video above shows the push-rod switch in action.
This observation leads us to the function of the push-rod switch on the left. The rod is spring-loaded. That is, the switch turns the light off when the door closes, holding the rod down, and is supposed to switch the light back on when the door is opened and the rod is depressed. We hypothesized that perhaps the switch mechanism was stuck and the spring did not release it when the rod was depressed. To test this idea, we squirted a tiny amount of light spray oil like WD-40® into the small gap between the rod and the switch cover, and sure enough our compartment light is back. Enjoy this otherwise fantastic fridge and good luck with aiming the ice cubes!