2008 grand prix gxp how to reset the computer

[stafphoto]

Hello new to the forums. I just got done helping a buddy replace an alternator on his 2008 pontiac grand prix gxp. When he went to try starting the car back up the horn started to honk and the lights came on. I'm assuming the computer needs to be reset and if so how would I do this? Thanks for any help.

[Scottydoggs]

sounds like an alarm went off when you hooked back up the battery.


other then that, you got it hooked up right?

[stafphoto]

We never unhooked the battery the replace the alternator as it was run down do to the alternator failing in the first place. So we hooked a jump box to the car and tried starting it that way. You could hear the starter clicking but it wouldn't start and the horn honked and the lights came on. I read about this happening to somebody else and they said a computer reset worked but I don't know how to go about doing this? You just undo the battery for a half hour and hook it back up?

[Scottydoggs]

un hooking the battery is the only way i know to re set a pcm. leave unhooked for like 30 minutes or longer.

[stafphoto]

Pretty much figured that. Will give it a try thanks.

[Scottydoggs]

when you say lights and horn come on, you mean they work? or they start to flash and sound off?

could just be a dead battery. or even a loose battery terminal. if the lights and horn just work.

[stafphoto]

Yes they were sounding off and flashing. But I had read somewhere else about somebody having there car do the same thing after a dead battery and they had to reset the computer and everything was fine.

[Scottydoggs]

the car have an alarm too? that could be what needs to be reset.

them 04 up cars got more electronics going on. that just may work.

[stafphoto]

That I'm not sure of. If it does how would you reset that?

[Scottydoggs]

if it is the factory alarm a pcm rest would be the only thing i can think of.

im no fan of electronics. they make my head hurt.

[stafphoto]

I hear you on that one. I'll have to wait until later tonight to see if the reset works or not. My buddy is at work.