2008 Tahoe Service Charging System

Stage2Tahoe · Dec 14, 2023

Just bought an 08 Tahoe 90k on the odometer. It has the flex fuel 5.3, 4L60e, 2wd, and has the LS trim package. I have had problems with the Charging System since I got it home. I took the Alternator and Battery to have them tested and they both passed so I reinstalled them. The Service Charging System came back. I went over the connections again and found the battery terminals were still a little loose. I fixed that problem and it was ok for a couple of days. I was then on the interstate and had to accelerate hard and it kicked the SCS again. It corrected itself then did it again about 15 minutes later (Every time the SCS popped up the voltage gauge dropped to around 12 volts). I did some research and found that a passing test on the Alternator doesn't mean it is working properly so I replaced it. Everything has been fine putting around town until this morning when I drove to work. I was on the interstate running 70. I eased on the gas and as I eased off of the pedal the voltage gauge dropped just below the 14 staying there for another 10 minutes not returning to where its suppose to be (In my opinion)

Is there something I am missing in the system that I need to check? I don't know much about the 08 system, but I know how the charging system is suppose to work. Something doesn't seem right. Any help would be greatfully appreciated.

strutaeng · Dec 14, 2023

These charging systems are pulse width modulated by the PCM and the alternator duty cycle varies based on electrical load and engine RPM.

I had an issue on our '13 Town and Country minivan where the alternator wouldn't charge. I foolishly replaced the alternator, which wasn't the problem. I wound up buying an older scope and determined the PCM wasn't commanding charge. PCM replacement fixed the issue.

I would say look up a charging wiring diagram and inspect all of the related wires. Sounds like something is intermittently not making good contact.

Geotrash · Dec 14, 2023

Stage2Tahoe said:
Just bought an 08 Tahoe 90k on the odometer. It has the flex fuel 5.3, 4L60e, 2wd, and has the LS trim package. I have had problems with the Charging System since I got it home. I took the Alternator and Battery to have them tested and they both passed so I reinstalled them. The Service Charging System came back. I went over the connections again and found the battery terminals were still a little loose. I fixed that problem and it was ok for a couple of days. I was then on the interstate and had to accelerate hard and it kicked the SCS again. It corrected itself then did it again about 15 minutes later (Every time the SCS popped up the voltage gauge dropped to around 12 volts). I did some research and found that a passing test on the Alternator doesn't mean it is working properly so I replaced it. Everything has been fine putting around town until this morning when I drove to work. I was on the interstate running 70. I eased on the gas and as I eased off of the pedal the voltage gauge dropped just below the 14 staying there for another 10 minutes not returning to where its suppose to be (In my opinion)

Is there something I am missing in the system that I need to check? I don't know much about the 08 system, but I know how the charging system is suppose to work. Something doesn't seem right. Any help would be greatfully appreciated.

If you're not getting the error any more, then I would consider what you're seeing normal. The computer switches off the alternator when it senses the battery voltage to be high enough. It's a fuel saving feature that sometimes freaks people out because the voltage gauge drops below the center mark when the alternator switches off. I notice it on both of mine - especially after doing a lot of highway driving on any given day.

Joseph Garcia · Dec 14, 2023

^^^^^x2^^^^^ My 07 Yukon XL Denali does the same thing. It is normal operation, as long as you have no dash trouble lights or codes.

Stage2Tahoe · Dec 14, 2023

I appreciate the feed back. I have read information on it, but its hard to not be skeptical. My 03 is down waiting for me to get the new motor built, and I had to find something to drive. Its hard going from older to newer because of the changes in the system. I am picking up on everything that is different with the powertrain and watching the gauges. With the 03 if the volts read around a steady 14.5.

swathdiver · Dec 14, 2023

Stage2Tahoe said:
Just bought an 08 Tahoe 90k on the odometer. It has the flex fuel 5.3, 4L60e, 2wd, and has the LS trim package. I have had problems with the Charging System since I got it home. I took the Alternator and Battery to have them tested and they both passed so I reinstalled them. The Service Charging System came back. I went over the connections again and found the battery terminals were still a little loose. I fixed that problem and it was ok for a couple of days. I was then on the interstate and had to accelerate hard and it kicked the SCS again. It corrected itself then did it again about 15 minutes later (Every time the SCS popped up the voltage gauge dropped to around 12 volts). I did some research and found that a passing test on the Alternator doesn't mean it is working properly so I replaced it. Everything has been fine putting around town until this morning when I drove to work. I was on the interstate running 70. I eased on the gas and as I eased off of the pedal the voltage gauge dropped just below the 14 staying there for another 10 minutes not returning to where its suppose to be (In my opinion)

Is there something I am missing in the system that I need to check? I don't know much about the 08 system, but I know how the charging system is suppose to work. Something doesn't seem right. Any help would be greatfully appreciated.

Get an OBDII adapter and download the Torque Pro app to your android or Car Scanner if IPhone. The car scanner app can see BCM codes which is where the code related to the message would be stored.

Having said that, that message usually refers to the alternator. How old is the battery? Auto Parts stores are notorious for generating false positives when testing batteries and alternators.

Your 2003 does not have EPM (Electronic Power Management) or RVC (Regulated Voltage Control). Look up those terms and do some reading to understand how they work. The were designed to extend the life of the battery and squeeze more efficiency out of the engine. Unplugging the 3-pin connector on the negative wire right off the battery puts the alternator to charge like your old car.

Stage2Tahoe · Dec 15, 2023

I have HPTuners so tuning won't be an issue if I have to go that far. I did hook up my OBDII scanner to verify the vin and make sure there were no hidden codes, and everything is clear.

From what I can tell the battery is new. I have not verified the manufacture date, but its a duralast gold and the posts still look new.

As for your last response for the EPM system.... The Tahoe has DOD/AFM. Would Unplugging the 3-pin connector have an adverse affect on that? I want to shut it off to be honest so I can try to reduce a chance for lifter failure and get more consistant feed back on how it is running. I don't like all this extra stuff. I know why they designed the system, but It I want a 4 cylinder then I will go buy one.

Writefast · Aug 13, 2024

Let me resurrect this thread. My 07 Yukon is doing something very similar to this.

Stage2Tahoe said:
I have HPTuners so tuning won't be an issue if I have to go that far. I did hook up my OBDII scanner to verify the vin and make sure there were no hidden codes, and everything is clear.

From what I can tell the battery is new. I have not verified the manufacture date, but its a duralast gold and the posts still look new.

As for your last response for the EPM system.... The Tahoe has DOD/AFM. Would Unplugging the 3-pin connector have an adverse affect on that? I want to shut it off to be honest so I can try to reduce a chance for lifter failure and get more consistant feed back on how it is running. I don't like all this extra stuff. I know why they designed the system, but It I want a 4 cylinder then I will go buy one.

Let me resurrect this thread. My 07 Yukon is doing something very similar to this. I also replaced the alt and it’s still not charging right to the point that the parts store is telling me that this alt is also reporting that it is failing. Did you get this resolved?

Stage2Tahoe · Sep 3, 2024

I did get my issue resolved. I had to replace my alternator but I have found that the alternator on my Tahoe fluctuates depending on load on the system and if the headlights are on/off. I don’t have the automatic light sensor installed right now so my headlights are always on unless I manually deactivate. When they are off I usually run at around 12-13 volts output. When I turn the headlights on or run the rear a/c it will jump to 14+, and from time to time it will rise or fall if the battery looses any charge.

Just Fishing · Sep 3, 2024

I haven't had to deal with this in the Tahoe yet, however my 07 jeep wrangler with the 3.8 had an issue where the PCM was telling it to charge.
the damn thing was hitting 16-18 volts!
Caused really weird things to happen.

Diagnosing it, everything pointed to the ECM.
There are other issues that will need to be addressed one day, so I'll probably end up having it replaced/rebuilt at some point anyways.

I finally bought this bypass kit from alternatorman, it gave me an external regulator and a driver that I install into the stock alt.
I had to use HPTuners to disable the alternator monitoring since the ECM no longer controls it, their little resistor kit didn't bypass the battery light, but HPTuners did. :happy160:

That fixed all of the issues; however, I'm now getting some pulsating things happening at idle with the lights on. :jester:

I'm pretty sure that the autozone special alt that the jeep came with is the cause there. :emotions34:

2008 Tahoe Service Charging System

Stage2Tahoe

Member

strutaeng

Full Access Member

Geotrash

Dave

Joseph Garcia

Stage2Tahoe

Member

swathdiver

Full Access Member

Stage2Tahoe

Member

Writefast

Full Access Member

Stage2Tahoe

Member

Just Fishing

Can't fix stupid

Similar threads

Forum statistics

Latest posts