Engine light on in my 2004 grand prix gt. says its heater circuit. what would cause this and how do i fix it?

SOURCE: how to reset the "service engine soon" light on a 2001 pontiac grand prix gt

you can go to advance auto and use there scanner for free to clear the code its called an obd2 connection or when you disconnect your battery you can touch your black negative cable to your red positive cable that connects to the battery and it will completley drain everything and reset but warning you if your trying to get the car through emissions your gonna have to drive the car 50 or 100 miles after you disconnect the battery each time..

SOURCE: Changed thermostat, grand prix gt, check engine light still on?!?

check evap vent solenoid alot stick on these cars.

SOURCE: LOOKING FOR A FUSE BOX DIAGRAM FOR 2004 PONTIAC GRAND PRIX GT

It's under the hood, on the driver's side, under a square, black box with a lightning symbol on it. Loosen the flower-shaped screw that holds the lid of the box down, remove the lid, flip it upside down and when you look at the inside of the lid, you'll see a map of all your car's fuses. There's also a fuse diagram on the very end of the dash, but it's accessible only when you open the driver's side door. When you're driving, that end of the dash is blocked by the closed door.

SOURCE: 2003 Pontiac Grand Prix SE 6 Cyl - Cooling Fan Not Operating

the fan motor could just be bad, you can test this by removing the fan and connecting a wire to each terminal and to a battery. the wires hooked up one way will spin the fan and the other way will spin the fan backwards so you cant hook it up wrong. I hope that helps you out!

SOURCE: I have a 2004 grand prix gt and sometimes on start it stalls

Take your car to a dealer and tell them to "clean the throttle body" Known problem for this year. It will solve your issue.