A few weeks ago I had a recurring problem with my 2010 Jetta TDI which caused the check engine light to turn on. Fearing the worst I contacted VW only to learn that this merely indicates an emissions issue. Apparently, its only when the engine light blinks that the driver should panic stop the vehicle for fear of imminent doom.
Once I dutifully delivered the vehicle to the dealer they hooked up the magic diagnostic computer. As far as I can tell this mystical device is essentially a USB dongle and a laptop computer. This modern oracle revealed that one of the injectors had failed to deliver its due share of fuel to the engine. Diagnosis: “You probably got some bad fuel.”
So the next day, yes, that’s right, the light is on again. Another trip to the dealer and the same diagnosis. Solution: Finish the tank of fuel and run another one through it. If the injector is bad it will continue to be bad, if it’s fuel it will probably go away. Next day, light comes on again, but I ignore it. Fast forward to last week and about half way through the new tank of fuel… light goes out. 
After speaking with the service manager, we agreed to monitor, but that it probably really was just bad fuel.
Through this whole adventure, I found myself wondering why the multifunction display in the middle of the dashboard can’t provide this information directly? Why can’t I push a button and have the car show the code information right on the screen? “No”, you say, “if they did that, then we wouldn’t be able to pay the dealer $75 to do it for us.”
So today, I’m on my way home, and what do I discover the German engineers have decided is worth my immediate attention:
There’s no need to inform the user about the inner workings of the engine, that ancillary system that MAKES THE CAR GO. The license plate lights: yes, a special light-shaped indicator and diagnostic text.