Stock alarm aux. channel

[n8huntsman]

I have the factory alarm. The key fob doesnt have an aux. button and I would like to have one. I know that some GM vehicles come with the extra button. Could I simply get one of those key fobs or do i need to change the entire module?

[GnatGoSplat]

Yes, the key fobs with the extra button will work.

BUT there is no extra channel if this is a current body style.

I've scoped out ALL the pins of the BCM with my meter... all the used and unused ones. The 4th button won't do a thing. The only place where it does anything is the serial data link between the receiver and BCM. There is serial data being transmit from the keyless receiver to the BCM when the 4th button is pressed, but the BCM doesn't do anything with it. I don't know if you can get the BCM reprogrammed to make the 4th button an aux channel or not. I suppose if you were a really smart guy you could build a circuit with a PIC microcontroller that watches the serial data link for the specific codes generated by that 4th button and grounds an output for the extra channel. I've thought about doing that, but I don't know anything about PIC programming.