Yes , having the vehicle checked for DTC'S - diagnostic trouble code's should always be the first step in diagnostic process when any warning lamps are lit on the instrument cluster . Would be best to have someone with a professional type scanner , that can view engine sensor data . The engine coolant temp. sensor is a input to the PCM - engine computer . Can see what the actual temp. of the engine is . GM had bad stepper motors inside the instrument cluster's 2003 to 2006 , these stepper motors control the gauge needles . Testing what the real temp is an not going by temp gauge . harbor freight tools sells a tool under $30 bucks that can check engine temp . Infrared Laser Thermometer .. Point it at the thermostat housing . Can use it to tell what temp. the thermostat open . But , testing is the key ! Not guessing .
SOURCE: 1996 Pontiac Grand Am / Overheating
How's your oil? Is the level high, or is the color milky? You've basically replaced your cooling system, all that CAN be wrong would be a corroded block [unrelated to anything you mentioned] or an internal leak. If the heat sensor loses contact with the coolant, it'll go nuts like that. And I'm guessing that could trigger the computer to go into panic mode. I suspect a leaking head gasket. Not that bad if you fix it yourself or know someone who will do it for friendship.
SOURCE: 1996 Pontiac Grand Am overheating
If its the 3.1L it could be your intake manifold gasket , the material used for the gasket does not react well with GM's Dex-Cool antifreeze. The leak may not be apparent at first, but I would pressure test the cooling system. If you look at the front of the motor by the belts , try to peek down at the intake manifold and check for slight seapage to an obvious leak.
If its either of the Quad-4's they were notorious for heads warping or cracking.
SOURCE: 1999 Pontiac Grand Prix Overheating
I had trouble with overheating on my 2000 Grand Am, The dealer could not even resolve the issue,(they wanted to replace the intake gaskets)...I knew that was not the issue, no air leaks or water leaking there; so I sit down to think; what are the causes of overheating. Thermostat sticking - nope not it, water circulates, Water leak - nope not it, has water stays until it gets too hot and goes out overflow, fans working - yep...hummmm the only other thing I could think of was losing of water pressure, yep that's it - the cap on the coolant tank was going bad, got a new cap ($8.00) replaced the old one and no more trouble going on 6 months now.
Hope this may solve your issue.
SOURCE: 98 Pontiac Grand Prix Overheating
YOU NEED TO REPLACE THE UPPER INTAKE MANIFOLD. ALSO, YOU WILL NEED TO REPLACE THE LOWER INTAKE MANIFOLD GASKETS. THIS IS A MANUFACTURING FLAW. THE PLASTIC INTAKE CRACKS CAUSING AN INTERNAL COOLANT LEAK. YOU CAN RESEARCH THIS ON LINE.
SOURCE: HELP!! Having electrical issues with my 2005 Pontiac
electical is hard to diagnose with out being there. i would treat each problem seperately. first you will need to test the engine temp gauge sending unit. in a dealership this is easy with a scanner they can run a sweep test to se if the gauges are responding.you don't want the engine to over heat if the gauge is not working. next problem the dome light should be easy to fixe does the dome light work with the dome switch?remove the bulb and with the doors open and switch on check for voltage, if voltage check connection and or replace bulb. if no voltage check fuses for voltage.last will need to have the dtc po243 checked out by a repair shop. i hope this will help.
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have u stopped by ur local parts store and had the codes read. sometimes when something like this happens u have to have it reset and then see if it sets it again. have the code cleared if its from the overheating. just from my experience not an expert.
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