Running a BCM as stand-Alone? [Archive] - Forum


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04-29-2008, 01:29 PM
I have been lerking the forums ever since i picked up my GA GT from the dealership, and i do have to say this site is awsome!

Now for the question, I have recently accurired and installed seats from a 2004 Grand Prix GT (leather/heated/power). They are awsome seats, But I ran into a snag. I know that heated seats need a computer of some sort to control them so they do not catch on fire, and in the GP's case, It's BCM controls them.

The question I am asking is if i run the BCM as a stand-alone(As in only the power/ground/and seats) hooked up to it, will it still work?


04-29-2008, 02:29 PM
Can't help you but I wanna see this man..

04-29-2008, 03:10 PM
I think that is the kind of thing you'll just have to try.. I don't see why it wouldn't work if the proper inputs were wired up. It shouldn't affect seat heater function if the class 2 bus isn't hooked up along w/ all of the other inputs

Most likely easier and cheaper to get aftermarket heaters.

04-29-2008, 03:16 PM
The thing is is i may beable to get the bcm/switchs for cheap >25$. (hopefully)

04-29-2008, 03:20 PM
In that case, go for it. the service manual for an 04 gp will have the pinouts

04-29-2008, 03:38 PM
Well, this is what i see:

BCM to seat:

The seat thermoresistors, low refrenceces..

The power to the seat heaters to provided by a relay, the control side is controlled by the BCM, the switched side looks like it is constantly powered by the main orn power wire, and when the relay is energized, it powers the seat heaters.

Now it looks like the heated seat switch is connected to the BCM by a class 2 wire, now I am confused how i can splice that, can i just cut and solder, or is that super special kinda wire?

04-29-2008, 05:00 PM
Alldata is your friend :)

05-01-2008, 07:07 PM
got the BCM and the controls; now i have a question, can i use the gp's hvac controls in place of the ga's?

also, I can power the hvac controls, as in make the lights light for the seats, but when I connect the bcm data link to the hvac data link, I cannot make the light light....


05-01-2008, 09:53 PM
No to the control head. The GA uses vacuum controls while the GP has electric doors.

The reason you can't get the heated seats to work is that the BCM is looking for a discreet ignition switch voltage from the GP's ignition switch to tell it to power up. The BCM in later model grand prix's actually acts like the ignition switch for the whole car. There's a 5v signal that goes to the switch behind the ignition cylinder and passes through a certain resistor based on the key's position. The change in voltage then tells the BCM what power mode is desired.

05-03-2008, 05:07 PM
Ok, So how can i duplicate that?

And right now, i only have power and ground hooked up.

thanls, that makes sense now, becuse the bcm has an ign 1 and 3 hook up to it..

05-03-2008, 05:19 PM
So I am looking at the GA's BCM, and it has a ing1 and 3 connection, can I use that?

05-03-2008, 06:54 PM
So I am looking at the GA's BCM, and it has a ing1 and 3 connection, can I use that?

like others have said, give it a shot and see what's up. Almost nobody here has tried to use another car's BCM for something like heated seats.