I have an 1991 300SEL. When I drive, the check engine light comes on for about 15 seconds and then disappears. My hunch is that the O2 sensor needs to be replaced. Please help. Is my hunch correct? What does the sensor look like and what is the correct procedure to replace it? Any help would be appreciated b/c I want to save a few bucks. Thanks a bunch. By the way, if I replace the sensor,do I have to get the light reset since it goes off by itself now?