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OK. so i guess we see what is going on here.

previous owner disabled the P0621 and P0622 codes in the ECM and wired up a different alternator, because he was an a-hole.
 

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if you want to find those wires, it looks like they split out of the engine harness at the same spot the MAF harness does. might want to dig around in there. you're going to need someone with hptuners to turn the codes back on, and to find a replacment connector if the PO didn't cut it off the harness.
 

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Discussion Starter #44
K well would that tuning remain if I used a handheld (Diablo tune)?
Let me take a pic of spliced wires, have to think they used the original alt wires
 

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it might overwrite it.

K well would that tuning remain if I used a handheld (Diablo tune)?
Let me take a pic of spliced wires, have to think they used the original alt wires
not sure.

i think i might have found the purple/white and brown connector purpose. it's definitaly not a ground, it's just taped up with them. gonna make sure before i post.

EDIT:
Ok, it's actually a dingy looking purple, and i think it goes to the starter solenoid. which is odd that you would have that disconnected... how the smurf would you start your car...
 

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Discussion Starter #46
Sorry. I just disconnected it to see if it came off the battery.
Here’s my 06 alt wires and the 05 in question.
So they just clipped off the connector for this non factory alt and now it seems I need to know why either terminal F isn’t reporting out or if there is a break in the line.
 

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It's not going to "report" anything with an older alternator. ECM expects a PWM signal from the F terminal, and watches the voltage (that it switches on via a high side driver) on the L terminal. The right alternator will do that. Whatever alternator you have hooked up isn't.

So swap the 05/06 specific connector and get the 05/06 alternator and you should be fine.

Unless that wrong alternator fried some part of the ECM. Pray that it didn't.
 

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Discussion Starter #48
Yeah bruh, could be anything at this point. I’d be somewhat impressed if the PO hacked this up to do what they had to to get the car going on a budget.
not so much if they clipped the connector and took a 50/50 shot of plug and play to see what worked frying that pin ckt in the process.

since I don’t plan on keeping this car and the setup technically is functional I’m good with either letting it be unless I can find a used alt.
I’ve considered taking the alt off my ‘06 to rule out the alt or even fix it.

thx for looking into this for me nothubert & mcnaughty. I’ll report back if I make progress.
 

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Sorry. I just disconnected it to see if it came off the battery.
Here’s my 06 alt wires and the 05 in question.
So they just clipped off the connector for this non factory alt and now it seems I need to know why either terminal F isn’t reporting out or if there is a break in the line.
the number on the label on the side of the alt is for a reman 2004 GTO alternator.

what i don't get is why they did that, unless someone just gave them a free alternator. there's not much price difference between the 2004 and 2005/2006 alternators.

or they bought it not knowing that the 05/06 had RVC alts and figured, "stupid GM changed the plug and charged more money, i'm smarter than them, i'll fix this!"

then BOOOPBEEEEPBOOOOPBOOOOPBOOOP "check alternator"

:mrrg:
 

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Discussion Starter #50
Ah ok, good to know. I google searched that # before and didn’t come up with anything.

i’ll likely swap alts and hope for no beeps
 

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Discussion Starter #51
Following up to close this case.
The situation:
Have an ‘04 GTO alt in my ‘05.
P.O. cut the connector off and wired the orange excite wire from the harness to the ‘04 alt to turn it on. It worked and produced 14.xV. The other pin was wired to the ecm-cluster circuit but the ‘04 alt doesn’t produce the signal that the ecm is looking for like the LS2 alt does.

As such the battery will get charged but the cluster will give a check alt message.

the hack for this would be to tap off a 12V circuit with an inline resistor to trick the ecm/cluster. This was proven by placing a test light off the battery to the ecm/cluster wire if the alt harness. Bam -check alt message gone.

I thought I’d be able to tap off the excite wire feeding the alt to turn it on but this isn’t a constant voltage source. I read somewhere that it’s a modulated signal at 5 or 7 volts so I’d have to run a dedicated wire from a switched source to do the ecm/cluster trick.

At this point I decided to return the system back to stock and stole my alt from my ‘06, bought the stock connector and all operates as it should in stock fashion now.
Thx for all who chimed in before.
 
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