Computers on 2004 Grand Prix

[gto421]

Hello i am trying to see if someone can tell me what the different computers on my 2004 grand prix operate. For instance what the the ECM control? What does the BCM control and What does the PCM control. Having a problem with the cooling fans operating properly. Changed the coolant temperature sensor no air in the system. So the mechanic says it is one of the computers. But not sure which one with our running a diagnostic check on the car.
So i someone can tell be if it is the ECM that controls when the fans turn on when they should or is it one of the other computers? The fan on the drivers side comes on when the ac is turned on but then turns off when the gauge gets to the half way point on the gauge and will not come back on. Right now it is direct wired. Also the ABS lights and the traction control lights have been on the dash for a while and the lights where the ac controls are flash at night when the head lights come on? I know i have a haunted car but i love it still.

[Fivefingerdeathpunch]

ECM = PCM. That controls anything engine related. Fuel, air, fans, transmission etc.

BCM is body control, so anything inside the car like windows, locks, blower motor etc etc.


What makes you think you have a problem with the fans?

If they come on with the AC they are working, if you unplug the coolant temp sensor and both come on they are working correctly.

They come on at a higher temp than you think, around 212 and 228 (high speed). Likely you car is not even getting much above 200ish and thus the fans will never come on. The stock dash gauge is not a proper way to tell temps.

[gto421]

the problem is that they do not come on when the sensor is unplugged and the gauge does not registar. The first fan with two speeds will come on when the ac is on but when the car gets to the half line mark the fan shuts off and the other fan never comes on. the fans should not shut off when the car is hot. we replaced the sensor twice and does the same thing and the mechanic at the shop has checked all the relays and fuses. And there are 3 computers on my 2004 the ECM the BCM and the PCM the ECM regulates the cooling fans oh it is getting above 200 if i dont get it shut off it will red line from stoping a starting in traffic. I even changed out the thermostat again and am loosing no water.

[Fivefingerdeathpunch]

Just to clarify again, you only have 2 computers. The ECM is the PCM, they mean the exact same thing. The PCM/ECM controls everything fan related aswell as engine related.

You could try swapping computers with another car on the same style. Any 04-05 computer will work aslong as the motor is still the same, a 06-07 could work too I think, just the gas gauge would rear backwards during the test.


Otherwise if it's still overheating and you've changed the sensor and thermostat, likely the water pump has given up on life and stopped pumping enough coolant around to keep it cool. But get to that after you figure out why it's not reading on the dash etc.

[gto421]

The water pump was just changed. a few months ago.