Service Battery Charging System warning

[American]

Yes, it's a Chevy, so I think it's a fairly common problem so my question should be easy for most ..just not me.

I have a:
2010 Chevy Express 3500 V8 6.0l
Gas,of course. Standard build, not crazy electrical on the system.

Question: I have been getting this warning showing up on my dash "Service Battery Charging System warning". I first checked battery, battery posts, any connections to the frame. All cleaned and good. Went to AutoZone and got battery and alternator tested. Again, all good. Still getting message so I started up vehicle and took off negative battery post. Running fine. Turned on lights. Running fine. Then...

I turned on the big AC in the back, not the one that is standard with the heating in the front, but the big one in the back; and the vehicle shut down.

Is this an absolute that my alternator is bad or did I just overload my test? I am struggling to find the culprit and would be thankful for any expertise. Thank you. Doug

[Jolly Roger bus 223]

did the AC run when you got the bus?
do you have a seperate alternator to run the AC?

[American]

Thank you Jolly Roger. Yes, the AC has run all this time. We have had this bus for over 3 years, with minimal issues. It does not have a second alternator. I turned off the AC, hooked back up the negative cable and it fired up. (It did take an extra second but running nonetheless.)

[Rucker]

So the alternator 'works', but they system is sensing a low voltage condition, and a large load kills the engine.

I assume you still saw the service battery/charging system warnings showing throughout your testing?

Poor ground to the alternator is my vote. Might be the ground cable to the engine that needs to be checked.

Unless the alternator test was a false negative.

And do you have only one battery? Does the rig start fine otherwise?

I'm guessing the rear AC blower circuit is a red herring. It's probably fine but when the large relays in the aftermarket circuit panel kick in they drop system voltage below what the engine needs to run.

I'd look there to see if there are any signs of poor connections, frayed wires.

[American]

Originally Posted by Rucker

Poor ground to the alternator is my vote. Might be the ground cable to the engine that needs to be checked.

.

Thank you for your response. In the past, we had an issue with grounding and were able to track it down, clean and fix...but this time although it seems to be the same I do not know where to look

Is there a diagram for this model that shows all grounds?? I'm kind of kidding but it would be dumb not to ask. Google is leading me nowhere on this one. Thanks again

[BamaBus]

Were you able to resolve the past 90 amp breaker issue?

I know that you have had this bus for a while, but I wonder if someone replaced the alternator at one point based on a spec for the Express van only.

[American]

Hey BamaBus. Yes, it appears so. We have been slowly tracking down faulty wiring. Our oil pressure dropped in one day by about 10psi. All of this is trying to figure out what is happening there. It seems electrical because I have ruled out most mechanical. Thanks for asking.

[Jolly Roger bus 223]

a haynes are chiltons manual will give you most of the chevy side wiring diagrams but no telling what the bus body manufacturer did.
my 04 express manual covers 98-2010.
someone had already pulled the rear A/C when i got the bus so i gutted the rest of it and installed dash air out of a suburban.
what i didnt realize at the time is the main A/C relay i took out also controlled the dash air command signal so i had to add a switch on the dash to command i cant remember which one now but it was either the high pressure switch or low pressure switch all it does is break the ground when off and closes the ground when on.

[Rucker]

Originally Posted by American

Thank you for your response. In the past, we had an issue with grounding and were able to track it down, clean and fix...but this time although it seems to be the same I do not know where to look

Is there a diagram for this model that shows all grounds?? I'm kind of kidding but it would be dumb not to ask. Google is leading me nowhere on this one. Thanks again

Yes-in the repair manual. Always a good investment.

I'd just look for a wire (sometimes just a flat braided wire no insulation) that runs from the engine block to the chassis and make sure there's not issue there. Some/many engines have grounds from the cylinder heads, apparently.

A simple Ohm test between the block and the negative post of the battery would tell you something. A high reading (maybe over 2 ohms) means poor ground.

I'm also wondering if despite the testing that alternator might be suspect.

[American]

I've moved this thread to this post. Thank you. https://www.skoolie.net/forums/f49/b...ons-44564.html