I have a 2002 deville with a leak in the middle of the water pump, it's not overheating and the heater in the car still blows hot, but the service engine light is on. Do I need to change the water pump or just a gasket?
A leaking water pump will not normally set a SES. Many past posts on changing Northstar pumps, some with pictures. If it's leaking from "the middle of the pump" do you mean around the pump pulley or on the other side, the water pump housing cover ?
Read the sticky thread at the top of the main Deville page - "How to pull codes" - and get to the link which has .......OBD-II in the URL. The codes and their meanings can be learned from the site, and one will be the code which set the SES.
Water pump time. Get the special socket with the retainer strap, or you'll need a spare gorilla to help hold the socket in the pump tangs. The pump comes out clockwise after removing the housing cover, usually with some sweat and, remembering the original tang location, goes back in counterclockwise. Might as well replace the tensioner and belt, too. No sense having to go back in.
While you are replacing the water pump. I would replace the old style water pump cover they are prone to leak and have been redesigned. I've had to replace them on both my 00 & 02 Deville's due to leakage.
Thanks to everyone for your help. It took a long time to do it. But I got the pump replaced and no signs of leaks. You guys were a life saver, I can't thank you enough. BTW, those stud bolts snap pretty easily if you try to tighten them too tight.