"Check Charging System"

[grasscutter]

Battery was at 12.0V on a cold start this morning. After idling a couple of minutes, it drops down to 11.9V and then a minute later to 11.8V. At 11.8V the "Check Charging System" comes on the dash. A few minutes later while still idling and the engine dropping from fast idle to regular idle, the battery voltage jumps to 14.7V. After 10 minutes of idling, the water temp is at 194F and the battery charge state holds steady at 14.5V. Dash says "Battery Voltage Normal." Battery is about a year old from Costco and the alternator is the original GM unit from the 2000 production year.

 

[WobblyElvis]

Just a guess.
The brushes in the alternator wear shorter and fail to make contact with the slip rings. They can be intermittent for a while, sometimes making contact sometimes not.

 

[ripcord]

Sounds like you're going to need an alternator. I would put a charger on your battery overnight as it takes a good 8 hours of driving to fully charge a low battery with a properly functioning alternator. 12.0V is only about 25% charged.

 

[Rand]

Just a guess.
The brushes in the alternator wear shorter and fail to make contact with the slip rings. They can be intermittent for a while, sometimes making contact sometimes not.

100% this is how the alternator in a 2005 ranger(owned by family)failed.

 

[14Accent]

100% this is how the alternator in a 2005 ranger failed.

Same as my '95 Seville: every so often the alternator would decide not to charge after a cold start, but after a few minutes it would suddenly come to life and be fine again for however long it felt like it. I let it go through the summer, but replaced it before the cold weather hit.

 

[Rand]

Same as my '95 Seville: every so often the alternator would decide not to charge after a cold start, but after a few minutes it would suddenly come to life and be fine again for however long it felt like it. I let it go through the summer, but replaced it before the cold weather hit.

The alternator on the ranger was about a 2 out of 10 for hard job.. so It got a parts store lifetime warranty replacement.
30min job tops is different than some of these new cars where its a major operation.

 

[Kira]

How did you know the battery was at 12.0V the morning this story began?
Did you measure the voltage before starting the car and at the ensuing minute marks?

If there's a dash readout, it might be yet another "processed signal" sent to a circuit which then translates it into a a voltage reading and/or warning message for the displays.

I suggest you measure at the battery as a helper reads the dashboard.

Me, I have an "original Volvo unit from the 2015 production year" and I get the occasional "low battery voltage" warning in the morning.
Most mornings I do not.
I actually haven't seen the warning enough times to establish a pattern.
What I may just do is throw my NOCO Genius10 on it overnight and see if the warning never returns. -EZ
Or maybe I should take a voltage reading every morning for a month .- LESS EZ

 

[14Accent]

The alternator on the ranger was about a 2 out of 10 for hard job.. so It got a parts store lifetime warranty replacement.
30min job tops is different than some of these new cars where its a major operation.

Wish I could say the same about the Cadillac. I don't consider it an overly difficult job, as much as others would have you believe otherwise, but it's a solid 2.5 hour job with the car on a hoist.

Given that, I stuck with a NOS Made in USA AC Delco alternator I found on eBay. $130 shipped, no core.

 

[grasscutter]

Sounds like you're going to need an alternator. I would put a charger on your battery overnight as it takes a good 8 hours of driving to fully charge a low battery with a properly functioning alternator. 12.0V is only about 25% charged.

What should the battery voltage be after sitting overnight?

Today driving across town on the freeway, the battery voltage got up to 14.9V and then went down to 14.8V.

At idle speeds on a warm engine it's constantly fluctuating between 14.6V and 14.7V. Today it got as low as 14.3V for a couple of seconds while I was parking the car in the garage and then hovered around 14.4V before settling down to 14.5V before shutting the engine off.

Is it normal for battery voltage to fluctuate by a 10th of a volt so much?

Car has a digital driver information center that displays battery voltage, coolant temp, oil pressure, and oil life percentage.

Battery lives underneath the back seat. This cold morning I was too lazy to pull the back seat out and put a voltmeter across the terminals.

This morning dipping down to 11.8V was alarming before it shot back up to 14.7V.

Seems like the alternator should come on sooner after a cold start.

 

[ripcord]

What should the battery voltage be after sitting overnight?

Today driving across town on the freeway, the battery voltage got up to 14.9V and then went down to 14.8V.

At idle speeds on a warm engine it's constantly fluctuating between 14.6V and 14.7V. Today it got as low as 14.3V for a couple of seconds while I was parking the car in the garage and then hovered around 14.4V before settling down to 14.5V before shutting the engine off.

Is it normal for battery voltage to fluctuate by a 10th of a volt so much?

Car has a digital driver information center that displays battery voltage, coolant temp, oil pressure, and oil life percentage.

Battery lives underneath the back seat. This cold morning I was too lazy to pull the back seat out and put a voltmeter across the terminals.

This morning dipping down to 11.8V was alarming before it shot back up to 14.7V.

Seems like the alternator should come on sooner after a cold start.

When the engine is running AND the alternator is functioning properly, those voltage numbers are normally what the alternator is putting out, not the actual battery state of charge. So when you see 14.7V, it means the alternator is charging the battery.

The actual battery state of charge would be what you see when the key is on, but before you start the car. A strong battery will read 12.6 or 12.7V then. The number that tells you the most about the state of the battery is the resting voltage first thing in the morning.

If the battery voltage drops down while you are cranking the engine over, that's totally normal, but it should jump up above 12.7V almost instantly after the engine starts and stay above 13.6V after a few seconds the rest of the time.

 

[grasscutter]

When the engine is running AND the alternator is functioning properly, those voltage numbers are normally what the alternator is putting out, not the actual battery state of charge. So when you see 14.7V, it means the alternator is charging the battery.

The actual battery state of charge would be what you see when the key is on, but before you start the car. A strong battery will read 12.6 or 12.7V then. The number that tells you the most about the state of the battery is the resting voltage first thing in the morning.

If the battery voltage drops down while you are cranking the engine over, that's totally normal, but it should jump up above 12.7V almost instantly after the engine starts and stay above 13.6V after a few seconds the rest of the time.

Right now after sitting for about four hours the battery voltage read 12.4V. That's with a volt meter instead of the dash readout.

I put a battery charger on the battery. A two amp trickle charge. I'll see what it reads in the morning. Thanks for your help.

 

[50yr Street Mech]

That alternator is almost 26 yrs old. How many miles on the vehicle ?

 

[grasscutter]

That alternator is almost 26 yrs old. How many miles on the vehicle ?

About 214,000

 

[50yr Street Mech]

WOW !!!! On a GM !!!!!! You hit lotto on that alternator ......You got you're money's worth out of it. Time for an alternator IMO.

 

[grasscutter]

This morning the battery voltage while still on the charger was 13.5V. The ammeter on the charger was down to zero which is good.

About an hour later I fire up the car to head to church. Dash meter said 11.8V after the start and the engine running.

Shortly there after the dash meter says 12.0V and stays at 12.0V all the way to church.

After church is over, I fire up the car and the dash meter goes immediately to 14.7V.

Before shutting the engine off at home in the garage, the dash meter settles on 14.5V.

About 30 minutes later I go out there and put a volt meter across the terminals. 12.66V.

This whole thing is weird. The battery seems to be taking a charge and the alternator seems to be putting out current to the battery, but there's that delay from the alternator immediately after starting the engine on a cold start that seems to be causing the battery voltage to momentarily drop down to 11.8V. Either that or the battery is losing a little charge overnight.

Somebody on the internet said that a faulty diode in the alternator could cause the battery to lose charge overnight.

 

[Snagglefoot]

Check your main ground cable from the engine to the frame. If it’s corroded, clean it up. If the wires are corroded to the point of detaching, replace the cable. There might be other ground cables as well. Check them all.

 

[ripcord]

It sounds like the alternator is only intermittently charging.

Good advise above about checking cables and connections.

 

[grasscutter]

Can I ask a dumb question? What tells the alternator to come on line and start charging the battery?

 

[ripcord]

Can I ask a dumb question? What tells the alternator to come on line and start charging the battery?

In modern cars, the ECU controls the duty cycle of the alternator. Usually, the ECU will command a higher voltage for a period of time before reducing it a bit after the battery has had time to recover from the startup draw.

In older vehicles, there is a voltage regulation circuit that determines how much DC voltage the alternator will produce. In most domestic vehicles this is internal to the alternator. The voltage output is relative to the voltage of the battery which is provided to the "S" terminal on the back of the alternator of most domestics. Typically, a lower the voltage provided on the "S" terminal increases the DC voltage output by the alternator up to a maximum set point, so the alternator will give a bit more if it sees the batter is low.

 

[grasscutter]

In modern cars, the ECU controls the duty cycle of the alternator. Usually, the ECU will command a higher voltage for a period of time before reducing it a bit after the battery has had time to recover from the startup draw.

In older vehicles, there is a voltage regulation circuit that determines how much DC voltage the alternator will produce. In most domestic vehicles this is internal to the alternator. The voltage output is relative to the voltage of the battery which is provided to the "S" terminal on the back of the alternator of most domestics. Typically, a lower the voltage provided on the "S" terminal increases the DC voltage output by the alternator up to a maximum set point, so the alternator will give a bit more if it sees the batter is low.

I found out from YouTube how to test an alternator. There's a positive post on the back of the alternator. I clamp my red lead from my voltmeter to the positive post. I clamp my black lead from my voltmeter to a good ground such as one of the upper strut mounting bolts. Earlier today I was getting a reading of 14.7 volts. About 20 minutes ago, I was getting a reading of 11.5 volts and then it dropped down to 11.48 volts a minute later. At this point, I have a good idea that my alternator is toast. Up until this point, the volt meter on the dash would read 11.8 volts after startup like it did today and then a few miles down the road the volt meter on the dash would jump to 14.7 volts.

This evening driving home from a job, the volt meter on the dash never got above 11.8 volts. Instead, it dropped down to 11.6 volts and then down 11.5 volts. When it got down to 11.4 volts, the "Battery Saver" light comes on the dash and the fan motor for the dash goes off. I'm assuming the PCM was the one that shut the fan off. As soon as I got home, I popped the hood and took a reading with my volt meter. 11.5 volts and then a few seconds later, goes down to 11.48 volts.

Normally something like this would not upset me at all, but I recently wiped out my checking account paying state property tax.