Alternator going bad?

[01BlueTahoeGuy]

Ok, about 6 months ago, I replace the battery in my 2015 Yukon SLT.

I changed it because I was having issues with the infotainment system, plus it was the original one.

We have been having issues again, so I am looking at it today.

I checked the battery voltage and it was 12.3v.

So I hooked my 4 amp battery charger to see what would happen.

It jumped to 13.6 and the indicator showed the battery was half charged.

I am fairly decent at understanding electrical, so on leaning towards the alternator not charging properly, I don’t have a tester.

My wife drives it daily, and it hasn’t failed to start since I replaced the battery.

Anyone else run into this?

 

[blondie70]

All looks ok to me...but the meter at half charge..maybe wacky meter ?

 

[Fless]

If you powered up (110v) your charger when the voltage went up, that's the charging voltage. But if your charger reads voltage without AC, then I don't know what to say.

Short trips don't allow for the charging system to completely fill the battery, so if your wife's trips aren't long enough to get things charged up after starting, you might want to consider taking longer drives.

 

[OR VietVet]

When checking the battery voltage that showed you 12.3 volts, start the engine with that meter hooked up and see if the voltage shown jumps up. That would indicate the alternator is charging but will not show the amps. You can watch the voltage and as the vehicle idles, turn on blower motor and headlights and whatever else you can turn on, like wipers. Watch for voltage to drop but then climb back up to what it showed at idle. That would indicate the voltage regulator is reacting to a load and catching up on the charging.

Should do a complete charge and then load test battery and see if it holds above 9.6 volts for 15 seconds.

 

[01BlueTahoeGuy]

Well, left the charger on it until is showed green.

Fired it up the with my multimeter hooked up, and it was at 14.3v.

Turned on the blower and such, no drop.

The drives are 45 to an hour each way.

But the infotainment system was working fine after I did all this ( which is why I was checking everything) after the battery was fully charged.

The rig had only sat for 12 to 14 hours….. so curious as to why the meter on my charger was reading low, it only took 20 to 30 minutes to top it off.

So now I am not sure what the issue is.

I know these things are super sensitive to battery voltages being low.

 

[swathdiver]

Keep an eye on it.

Without a Tech-2, a good way to check the battery's state of charge is to put the meter to it in the morning after it has sat all night. Check the voltage and ambient temperature against a chart and that will give you a close approximate state of charge. GM considers a battery wore out if the state of charge is below 65%.

The battery might need to have its plates de-sulfated so see if your tender/charger handles that. I got another year out of a battery with my tender and that battery had been run to the single digits dead a couple of times.

 

[01BlueTahoeGuy]

Will check.

This battery is an Interstate not even a year old…..

 

[the 18th letter]

I’ve read the battery cables on these can look fine but have corrosion inside, somewhere on the site there’s a post on how to test them. Corroded grounds have also been know to muck up the electrical system in these.

 

[01BlueTahoeGuy]

Ok, while out driving today, the voltage gage on the dash dropped to just above 9v a couple of times then went back to 14v.

I pulled the alternator out and took it to AutoZone and it tested as good.

I am wondering if there is an intermittent issue in the alternator, I have checked the cables, can’t find any corrosion and all the connections were tight.

I am leaning towards getting a new alternator, but am having sticker shock as the parts stores want 380 and up, Rockauto is 250.

Any thoughts or others troubleshooting anyone can recommend?

 

[OR VietVet]

You saw it intermittently working on the gauge. Attach a DVOM with long enough leads, and drive it again.

 

[01BlueTahoeGuy]

I don’t have long enough leads for that.

When I pulled the alternator, I checked the battery and it was at 12.3v.

Since this is the wife’s rig, and currently she is having to drive it 45 minutes to an hour away from home, I am hesitant to put this alternator back in it.

Given the other issues going on I am leaning heavily towards just replacing it.

The battery light never came on during this and the low out put was probably 20 minutes each time with no drivability issues.

 

[OR VietVet]

If is actually not charging correctly, intermittently, those injectors are firing off of the battery and so are a lot of other components. You can make leads extensions with some alligator clips and 12 gauge wire that is long enough to reach under the hood and snake in the cab and then attach the DVOM leads to them. Make sure that anything that is exposed does not touch where it shouldn't when driving.

Hell, if you have the right scanner, you can drive with it attached and watch the screen.

 

[01BlueTahoeGuy]

Thanks for the tips.

I put everything back together.

With the blower motor at max, the rear climate controls on, headlights on, it’s putting out 13.6 on the gage.

At idle it’s bouncing between 13.5 and 14.6v.

I am not sure what’s up.

All the gage electronics and gages are working, just the radio and radio control system seems to be on the fritz.

The clock on the upper right corner flashes, and I can’t get it to come on.

Maybe there is another gremlin somewhere.

 

[OR VietVet]

Check all related grounds?

 

[01BlueTahoeGuy]

I have checked all the grounds I am aware of.

If anyone has a diagram or list of them that would be great.

Other than the radio/audio control stack, everything else appears to be working fine.

I have let it idle for about 20 minutes with everything on and the volts have been between 13.5 and 14.6 on the gage and my meter.

The clock on the radio continues to flash as if there is a loos ground, but checking the voltage at the fuse for it and the amp show battery voltages.

I am lost at this point.

It’s running and driving fine.

 

[Rygrego]

Ok, about 6 months ago, I replace the battery in my 2015 Yukon SLT.

I changed it because I was having issues with the infotainment system, plus it was the original one.

We have been having issues again, so I am looking at it today.

I checked the battery voltage and it was 12.3v.

So I hooked my 4 amp battery charger to see what would happen.

It jumped to 13.6 and the indicator showed the battery was half charged.

I am fairly decent at understanding electrical, so on leaning towards the alternator not charging properly, I don’t have a tester.

My wife drives it daily, and it hasn’t failed to start since I replaced the battery.

Anyone else run into this?

The alternators in these and most modern vehicles charge only when commanded by the ECM for fuel economy. Low demand equals low output. Start the car turn on the headlights , A/C and any other loads and then read the output.

 

[01BlueTahoeGuy]

Honestly at this point I wish it was an old school system with two speakers, a power wire, a ground.

 

[OR VietVet]

It took a while for me to get used to the way they show charge now, depending on load. I had to have it explained to me and now I don't give it a second thought. Your alternator and system may well be working as designed and be just fine.

 

[Gearz]

The chager from Harbor Freight is on AMG is that what you have for a battery? You need to do a parasitic draw with a DVM and see what the truck is drawing which can be complicated. I had a AMG battery which caused many issues so I went back to a flooded battery and it made a huge difference. The alternator is pulse with modulated so it will only work under certain conditions. I have a 2011 Tahoe and Auto Zone had a alternator for new for $180 with lifetime warranty. The battery cables can be corroded underneath the plastic coating so a voltage drop or physical inspection is required. Instrument panel gauges are a possible electrical draw on the system especially when you said your gages were acting up.

 

[irwires]

Most likely you have corroded ground wires in several places. Especially the engine ground. GM vehicles are notorious for this. Most of the crimp terminals they use are open and exposed to the elements. You can check the resistance of the ground and power cables with a good quality meter.
Don't use something cheap as you will get poor readings. Follow the main cable from the battery negative to the engine block, disconnect it and measure the resistance end to end Should be almost nothing. Clean the block and reattach. You can do the same with the positive. Also most GM's have a copper ground strap at the back of the engine to the body. This usually rots away. The body ground could explain the info system problems. The more you drive the hotter connections get if they are corroded and become higher resistance connections. Also your alternator may drop to 9 volts at times. This will cause more drain on the battery and then it will go back to 13-14 volts.