I checekd the radiator. It's filled upto top. I also filled enough coolant in the reservoir bottle but my lights still stays on. this is what happens. When i start car in the morning it stays on for 5-7 minutes and after that it goes off. Could this be because of bad sensor? Where is the coolant level sensor in 1998 Grand Prix? Is this something i need to replace right away? By the way temperature stays within acceptable limits.