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Old 10-28-2013, 01:41 PM
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Default 2008 silverado alternator help

So the newer style GM trucks have EPM, which regulates the voltage charge from the alternator to the batteries based on what STOCK items are drawing power from the battery. So me, like many others, will have my battery at random levels of voltage based on if my lights, a/c, wipers, are on ect. Your system (aftermarket amps) do not effect this lame feature gm added. I hear there is a way to bypass the sensor that does this so my truck alt always charges at 14.4v

Does anybody know how to do this


Please help.
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Old 10-28-2013, 02:28 PM
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I might have read turn your headlights on......probably wrong though. Gm uses a amp sensor on the ground off the battery. I just said screw it and ran dual alternators. Or you could run a pre 2007 alternator oval plug and ignore the battery light on your dash
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Old 10-28-2013, 04:37 PM
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Turn on your headlights or put it in tow haul
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Old 10-28-2013, 04:43 PM
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Reminds me of this similar issue with Hondas and their "ELD". Probably works on a similar principle. I wonder how hard it is for you to get an external regulator?
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Old 10-28-2013, 06:09 PM
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Knew about the tow thing, but that changes your shift point and I don't like shifting that high. The headlight thing does not work %100 of the time. Does anybody know where this sensor is so I can remove it?
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Old 10-28-2013, 06:12 PM
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TThe sensor is likely integrated... try turning on the rear defrost if u have one... the switch alone should activate the alt computer wise if u wanna unhook it from working vs running all the time
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Old 10-28-2013, 06:39 PM
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tricking doesn't always work, most gm's when it isn't truly sensing the load it will not put out fully. IT must be limiting field current more or something.

in my 3.8l car when its charging 14.4 my alt does over 300a, but when it backs down, i turn my headlights on to trick it, then voltage goes up to 14.0v the alt will only do 150-200a at best until it reacts to the voltage drop and starts charging in the 15's. then its right back up around 300a output again. I've seen this in trailblazers as well. haven't tested any trucks, however.

send your alt in and have it converted to a pcm bypass setup and get rid of that pcm crap.
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Old 10-28-2013, 06:44 PM
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Quote:
Originally Posted by 72impala View Post
I hear there is a way to bypass the sensor that does this so my truck alt always charges at 14.4v
From Avalance Forum
Quote:
Generator Battery Control Module

The generator battery control module is a class 2 device. It communicates with the powertrain control module (PCM), instrument panel cluster and the body control module for electrical power management (EPM) operation. It is a serviceable component that is connected to the negative battery cable at the battery. It directly controls the generator field control circuit, charge indicator control, input to the generator. It continuously monitors the generator field duty cycle signal circuit and the battery voltage. If the generator battery control module loses communication with the PCM, the default voltage will be set to 13.8 volts and the module will set U1016. If the generator battery control module loses communication with the body control module (BCM), the module will set U1064.
You will have a check engine light but you can more than likely disconnect whatever plug is on the sensor on the stock ground wire.

If you need help take a picture and get back to us.


Additionally I found this

Quote:
The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5 volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.
Sounds like good news for the aftermarket.

Last edited by MaTT6387; 10-28-2013 at 06:55 PM.
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Old 10-28-2013, 07:00 PM
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I unplugged the 3 pin wire that is in a plastic module wrapped around the factory negative ground, nothing changed. Then I disconnected the factory ground (fine because I have big 3 done), and still no change??
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Old 10-28-2013, 07:17 PM
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This seems risky but maybe wire it up to a switch? I bear no responsibility in destroying your alternator.

How to bypass the Generator Battery Control Module - Fixya

If you ground the test point on the back of the alternator (near positive post) it will go full out. Remember if you run at full output constant, you will damage e.c.m., g.e.m., and battery.
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