Red Battery Light

[benjaminblazer]

Went on a quick trip to the store and the red battery light came on. First thought was to check charging level at battery, 14.8, battery with car off 12.8
Next I thought to unhook my aftermarket amps, light still appears.
My guess is it is still the alternator, I have an aftermarket 270 amp autotech alternator that has never given me problems for almost 3 years.
Any suggestions on what to check or look for would be much appreciated, thanks

 

[TJBaker57]

Does the warning lamp go completely off when the key is off?

 

[benjaminblazer]

Does the warning lamp go completely off when the key is off?

Yes

 

[budwich]

disconnect the plug at the alternator and then turn the key to ON (do not start).... is the light still on?

the purpose of this test is to isolate / reduce where the issue might lie.

 

[Mooseman]

Since the PCM has direct control of the alternator, something might have happened to the internals of the alternator even though it's still charging. You could try to scan for codes as there may be an underlying code that doesn't set off the CEL since it's not something affecting the engine or emissions.

What year is your truck? Does it have a SARVC attached to the negative battery cable? If so, it could be defective although I haven't heard of it throwing a battery light even when unplugged. All it does is reduce the charging rate and voltage when the battery is fully charged and the loads are low.

 

[benjaminblazer]

Since the PCM has direct control of the alternator, something might have happened to the internals of the alternator even though it's still charging. You could try to scan for codes as there may be an underlying code that doesn't set off the CEL since it's not something affecting the engine or emissions.

What year is your truck? Does it have a SARVC attached to the negative battery cable? If so, it could be defective although I haven't heard of it throwing a battery light even when unplugged. All it does is reduce the charging rate and voltage when the battery is fully charged and the loads are low.

2006, unsure if it has the sarvc, I dont think so though. I have the big 3 upgrade but only stock grounds are to the body and the engine block. Will try and scan today as well thank you

 

[benjaminblazer]

disconnect the plug at the alternator and then turn the key to ON (do not start).... is the light still on?

the purpose of this test is to isolate / reduce where the issue might lie.

Light does not come on, but car also isnt running and i think it has to be running to come on. Light doesn't come on right away when started but eventually shows up

 

[benjaminblazer]

Since the PCM has direct control of the alternator, something might have happened to the internals of the alternator even though it's still charging. You could try to scan for codes as there may be an underlying code that doesn't set off the CEL since it's not something affecting the engine or emissions.

What year is your truck? Does it have a SARVC attached to the negative battery cable? If so, it could be defective although I haven't heard of it throwing a battery light even when unplugged. All it does is reduce the charging rate and voltage when the battery is fully charged and the loads are low.

Scanned and dont see anything to do with electrical. Just a po171 code thats been here and there.

 

[benjaminblazer]

Since the PCM has direct control of the alternator, something might have happened to the internals of the alternator even though it's still charging. You could try to scan for codes as there may be an underlying code that doesn't set off the CEL since it's not something affecting the engine or emissions.

What year is your truck? Does it have a SARVC attached to the negative battery cable? If so, it could be defective although I haven't heard of it throwing a battery light even when unplugged. All it does is reduce the charging rate and voltage when the battery is fully charged and the loads are low.

Did one of these tests.. got "good battery" and this:

 

[Mooseman]

Voltage regulator in the alternator may have taken a permanent vacation. It's a little high but not crazy high but if it doesn't come down after a while, it could cook the battery. It should drop back down to ~13.5V without a SARVC. With, it can drop down to ~12.5V once the battery is charged and there is low power draw. However, since you have a non-stock alternator, the SARVC may not work with it. If you do have one, try unplugging it. It should be attached on the negative battery cable.

 

[benjaminblazer]

Voltage regulator in the alternator may have taken a permanent vacation. It's a little high but not crazy high but if it doesn't come down after a while, it could cook the battery. It should drop back down to ~13.5V without a SARVC. With, it can drop down to ~12.5V once the battery is charged and there is low power draw. However, since you have a non-stock alternator, the SARVC may not work with it. If you do have one, try unplugging it. It should be attached on the negative battery cable.

My battery has been charging this high since i got the alternator, thats what makes me wonder why its just now showing. Does my 2006 for sure have an SARVC? What would it look like, like I said i only see 2 wires from the battery negative cable.

 

[budwich]

Light does not come on, but car also isnt running and i think it has to be running to come on. Light doesn't come on right away when started but eventually shows up

That's not quite true.... the key in ON position does "setup" things.... like energizing the PCM among other things.

My guess at this point is that the alternator / charge control has issue. The system doesn't really have a way of determining the "health" of the wave form meaning that if you have lost a diode in the bridge then your waveform isn't really "good" for charging. That is just an example of potential issues.

Anyway, as mentioned by Mooseman, the voltages that you are seeing are somewhat suspect and based on the scanner "hint" is the point for attention. As for the SAVRC, the unit is at the negative cable at the battery and has a connector with multiple wires coming off of it which feeds the PCM.... easy to spot.

ADDED: a quick look at the GM SI appears to indicate no SAVRC.
I would do a close inspection of the connector at the alternator, only two of the 4 pins are used. Make sure that those pins are clean and seated well. The RD wire in the connector is the one doing the feedback of the system to the PCM which is causing the light.... I think.

 

[Mooseman]

After inspecting and checking everything, if you still have it, you could reinstall the original alternator if it was working fine when it was removed. This would prove if it's at fault or not. Could also take it out and have it tested at a parts store.

 

[budwich]

Could also take it out and have it tested at a parts store.

This may help but I am not sure the "off vehicle test" provide much more than a "turn on" mode and check the resulting voltage output. I don't know if they monitor the "feedback line" as that might take a bit more "science" because of the various alternators / makers out there.

My guess is that the alternator has a regulator issue resulting in a less than good "feedback" waveform that the PCM is "choking" on.... but it could be just a poor connection.

 

[benjaminblazer]

That's not quite true.... the key in ON position does "setup" things.... like energizing the PCM among other things.

My guess at this point is that the alternator / charge control has issue. The system doesn't really have a way of determining the "health" of the wave form meaning that if you have lost a diode in the bridge then your waveform isn't really "good" for charging. That is just an example of potential issues.

Anyway, as mentioned by Mooseman, the voltages that you are seeing are somewhat suspect and based on the scanner "hint" is the point for attention. As for the SAVRC, the unit is at the negative cable at the battery and has a connector with multiple wires coming off of it which feeds the PCM.... easy to spot.

ADDED: a quick look at the GM SI appears to indicate no SAVRC.
I would do a close inspection of the connector at the alternator, only two of the 4 pins are used. Make sure that those pins are clean and seated well. The RD wire in the connector is the one doing the feedback of the system to the PCM which is causing the light.... I think.

Yes I understand but the car should be on and running to see if the alternator has any issues right? Also like I said i have been charging at 14.8 for 4 years now. Why all of the sudden would that be causing the light to come on? Yeah I didnt think there was an SAVRC just because iv looked at the engine a billion times, id remember. Going to inspect the connector today. When I first installed the aftermarket alternator it had me put a blue wire onto the positive post of the alternator. Without it, the red battery light would show, could that have anything to do with it?

 

[benjaminblazer]

After inspecting and checking everything, if you still have it, you could reinstall the original alternator if it was working fine when it was removed. This would prove if it's at fault or not. Could also take it out and have it tested at a parts store.

Yeah I plan to do this, it will quickly show me if its the current alternator causing the light

 

[budwich]

Yes I understand but the car should be on and running to see if the alternator has any issues right? Also like I said i have been charging at 14.8 for 4 years now. Why all of the sudden would that be causing the light to come on? Yeah I didnt think there was an SAVRC just because iv looked at the engine a billion times, id remember. Going to inspect the connector today. When I first installed the aftermarket alternator it had me put a blue wire onto the positive post of the alternator. Without it, the red battery light would show, could that have anything to do with it?

the purpose of the test is to possibly eliminate any hard fault that might exist in the sense circuit... nothing to do with any specific testing of the alternator itself. There are other tests for that.

IF the battery light would have stay on, that points to other tests.

Anyway, hopefully your old alternator (why did you replace it?) will tell you more.

 

[benjaminblazer]

the purpose of the test is to possibly eliminate any hard fault that might exist in the sense circuit... nothing to do with any specific testing of the alternator itself. There are other tests for that.

IF the battery light would have stay on, that points to other tests.

Anyway, hopefully your old alternator (why did you replace it?) will tell you more.

I replaced it because I had a 6000 watt system in the trunk, the alternator was just one of the electrical upgrades to it

 

[benjaminblazer]

Changed the alternator, battery light went away, contacting the manufacturer now to see what they suggest. Just stumped at the fact the voltage was fine, what else does the alt need to do besides charge the battery at what its supposed to.

 

[budwich]

Not all voltages are "equal". You need a load tester or equivalent while monitoring the voltage signal along with the field signal. Your DC value is borderline with 15v being an over voltage condition. There are some checks with a meter for regulator failure.

What is the voltage measured with the old, now installed unit?

 

[benjaminblazer]

Not all voltages are "equal". You need a load tester or equivalent while monitoring the voltage signal along with the field signal. Your DC value is borderline with 15v being an over voltage condition. There are some checks with a meter for regulator failure.

I dont think charging at 14.8 could be the problem, bigger alternators are meant to be around that 15 voltage range to keep my amp with the voltage it needs to put out enough power.

 

[budwich]

Maybe.... but the spec for the truck is looking at a 15v limit. IF there is any "ripple", it is plausible that it could trgger the warning. I don't thinking charging of your battery at 15v ish is good for its long term health.