I recently filled the gas tank on my 1998 C230, 88K miles. When I got back into the car, the fuel gauge showed completely empty and the fuel light came on. It remained that way until the next time I started the car. Later that week, when the fuel was approximately at 3/4 of a tank, the gauge again showed empty and the fuel light came on again. This has happened on several, but not all, occasions since then, usually when I fill up. I'm confused about what's causing this and how to fix it. Is it an sensor, or an electronic issue? Any ideas or help would be much appreciated. Thanks!