That is the AIR system pump and it does just what it's name implies, pumping air into the exhaust stream to get the primary catalytic converters warmed up faster. Other than a light, there is nothing bad going to happen. Another thing I was going to mention in 240's block off plate for sale thread is that you can measure the resistance and put a giant power resistor in there to keep the light from coming on. I never got that far with my car so I couldn't tell you what size/rating/resistance needed. Hope this helps.