Anyone ever see this fault code? It sounds serious!

[Steve Cole]

So I got this error code- PO622 Generator F-Terminal Circuit

"Repair immediately if drivability issues are present. Threat to essential system components if not repaired as soon as possible."

The backstory- donor is a 2005 gen 3, 5.3 truck motor. truck has not been driven since the swap, just started in the garage as I am still finishing up the small details.

I think the issue is the choice of power wire for the computer, or maybe the wiring for the alternator. I used an existing 10 gauge wire for the main power supply. I don't remember if it was the wire for the alternator or the wire for the tach from the distributor, or what. I had a buddy over to help me get the wiring hooked up that day and it was his suggestion to use that wire, that's why I can't remember which one it is.

So what do I need to do to fix this? How should I run the power wire?

Thanks for any help with this, I am over my head at this point.

[clinebarger]

Not serious at all....

*Is the alternator charging?
*What is the battery voltage with the engine running?
*Are you running the factory 2005 alternator?
*Is the Regulator plugged in?

2005 1500's was the first year for the alternator control module, I generally segment swap these PCM's & run a 2500/3500 or 2004 & earlier 1500 alternator.

[Steve Cole]

Thanks for the quick reply Clinebarger!

As for your questions- I am running the factory 2005 alternator. I don't know if the battery is being charged by the alternator or what the battery voltage is while running because i have not run the motor more than a few seconds at a time because I don't have the radiator hooked up yet and I am trying to get the O/H tranny full of fluid, the cluster isn't installed yet etc. I just finished up the air intake yesterday. I wanted to figure out this fault code before I put the cluster in just in case it is a under dash wiring issue I need to correct.

You asked if the regulator was plugged in. I thought the alternator was internally regulated. Where is this regulator located? What about the Alt. control module, is it internal? TIA

[Steve Cole]

This HAS to be the reason for my fault code right? Nothing going to the battery. This is what happens when you stop working on something for a year then try to pick up where you left off!

[Steve Cole]

Originally Posted by clinebarger

Not serious at all


2005 1500's was the first year for the alternator control module, I generally segment swap these PCM's & run a 2500/3500 or 2004 & earlier 1500 alternator.

Hey Clinebarger,

Can you explain what you mean by segment swapping the PCM's and why you do that? Is the 2005 alternator prone to problems?

Thanks!

[truckdude239]

Originally Posted by Steve Cole

Hey Clinebarger,

Can you explain what you mean by segment swapping the PCM's and why you do that? Is the 2005 alternator prone to problems?

Thanks!

steve a segment swap is when they change part of the software in the ecm to run like something from a different year like in your case you dont have the alternator control module so the ecm is defaulting what it want the ecm to charge to 13.7v, if you have someone change the charging part of the computer software to say a 2004 alterantor software and use an 2004 alt then you proplay sovle most of your problems

[Steve Cole]

Thank you for that great explanation David, I get it now! About the alternator control module, is this something I should have taken from the donor truck?

I checked Auto Zone but they don't list one. I know where my donor truck is so I could go get it if I knew what it looked like. I figure this would be easier than trying to find someone to re-program my ECM.

[ls1nova71]

The GBCM is located on the negative battery cable, 6" or so from the battery terminal. There are several wires that go to it which can be easily hooked up, but there is one serial data wire that ties into the instrument cluster. I have never tried it, but have heard it will work without the instrument cluster wired in it.

[mongocanfly]

Yeah........that would do it...

[ls1nova71]

Yep! They haven't come up with wireless charging for cars yet!

[biketopia]

Love a good easy fix!!

[Steve Cole]

Does anyone ground their alternator case? Doing some web browsing I have seen several posts saying it should be done. I have never heard of this.

[AussieinNC]

There are some installations, not necessarily on LS or GM engines, that use isolating rubber bushes in the alternator case mount positions to minimize vibrations.....

In these cases a separate ground strap between the alternator case and the engine block is necessary for the system to charge....

I have seen these mainly on industrial equipment engines and diesels....

I think I remember seeing a ground placement screw on some GM alternators...but I am too lazy to go look in the shop !

[biketopia]

The bracketry the alt is mounted to is grounded if your other grounds are where they are supposed to be.

[Steve Cole]

Ok, I still have this issue. To answer Clinebarger's questions,- the battery appears to be fully topped off. I ran the motor about 5 minutes tonight and kept checking the battery with my meter. It stayed around 13.69 v the whole time. I ran it about 10 minutes the day before so I have to assume the alternator is charging the battery, otherwise it wouldn't be topped off. I don't know what he means by "is the regulator plugged in?"

This is a 2005 engine with the same alternator that came with it. I have a battery cable running from the + battery terminal to the starter, and a charge lead cable from the alternator to the + battery terminal. The - battery terminal runs to the engine block, the block to the frame and the chassis to the frame.
When I clear the fault code with my reader, the reader immediately rescans and the fault comes back.
I am in over my head with with this and would appreciate any suggestions what to check or look at.
Thanks.

[EVRLET]

This is straight from the 2005 factory manual.

[A1971Blazer]

I replaced the alternator on my LS1 with a 140 amp one...
when I wired the engine to test run it I plugged the single red wire from the harness into the alternator as it should be
ran a #8 wire from the terminal and just left the other end open (protected of course)
I fired the engine and checked the output on the wire...nothing...no voltage output
I then attached the wire directly to the battery I was using to run the engine...Immediately it jumped to 14.25V...(battery was a little weak)
I assume this means that the voltage sensing and control of the alternator by the PCM is working properly?

[ls1nova71]

If you are not running the GBCM, then this will happen. The PCM defaults to 13.7v all the time. I ran a truck this way for a while, not sure how long it will last this way though as I'm sure it will shorten the life of the alternator.

[Steve Cole]

Originally Posted by ls1nova71

If you are not running the GBCM, then this will happen. The PCM defaults to 13.7v all the time. I ran a truck this way for a while, not sure how long it will last this way though as I'm sure it will shorten the life of the alternator.

Trying not to sound stupid here, but what is a GBCM? How do you "run it"?

Thanks for the manual pages EVRLET, I couldn't read the wiring diagram though.

[AussieinNC]

Originally Posted by Steve Cole

Trying not to sound stupid here, but what is a GBCM? How do you "run it"?

Thanks for the manual pages EVRLET, I couldn't read the wiring diagram though.

GBCM...Generator Battery Control Module...I know they are not generators but whatever...

See for more details

https://www.gmfullsize.com/threads/g...iagram.313913/

[Steve Cole]

Thanks for clearing that up Aussie. I think my next step is to test the alternator to see if this is my problem. I hope it's not the ECM.

[ls1nova71]

Originally Posted by A1971Blazer

I replaced the alternator on my LS1 with a 140 amp one...
when I wired the engine to test run it I plugged the single red wire from the harness into the alternator as it should be
ran a #8 wire from the terminal and just left the other end open (protected of course)
I fired the engine and checked the output on the wire...nothing...no voltage output
I then attached the wire directly to the battery I was using to run the engine...Immediately it jumped to 14.25V...(battery was a little weak)
I assume this means that the voltage sensing and control of the alternator by the PCM is working properly?

Sounds like it is working. LS1's use a different kind of voltage sensing.

[EVRLET]

Hope this is better