Help Overcharging issue
Thread Starter
Instructor
Joined: Jul 2009
Posts: 148
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From: Ańasco Puerto Rico
Help Overcharging issue
Hi people
About March 2020 my 2005 Vette starts poor with low charging and a Service Charge System message on the DIC, well bring the car to a GM dealer after 2 weeks dealer says that the alternator and the ECM have to be replace, well buy new alternator but the ECM they do not have it and GM does not manufacture this part anymore. After 1 month making a lot of phone calls find an aftermarket one , then send my VIN to programend it. When receive it install it, and now the issue is it is overcharging 14 1/2 to 15 call back the vendor and returned it to them and they send another one and install it and have the same issue and again it is overcharging causing to dry 2 batteries cells also car battery is a new AC DELCO buyed together with alternator. Hope you people can help me with this matter
THANKS
About March 2020 my 2005 Vette starts poor with low charging and a Service Charge System message on the DIC, well bring the car to a GM dealer after 2 weeks dealer says that the alternator and the ECM have to be replace, well buy new alternator but the ECM they do not have it and GM does not manufacture this part anymore. After 1 month making a lot of phone calls find an aftermarket one , then send my VIN to programend it. When receive it install it, and now the issue is it is overcharging 14 1/2 to 15 call back the vendor and returned it to them and they send another one and install it and have the same issue and again it is overcharging causing to dry 2 batteries cells also car battery is a new AC DELCO buyed together with alternator. Hope you people can help me with this matter
THANKS
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,418
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From: Cape Coral, Florida
Sometimes an “elevated“ ground may cause this...try taking a jumper cable and clamp it to the alternator case to battery negative and if no good try from battery negative to the engine block...see if that works !!...your ECM was probably fine !!
Last edited by C5 Diag; Jul 29, 2020 at 05:47 PM.
Race Director
Joined: Dec 2013
Posts: 12,501
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Seen too many C6 rebuilt alternators with the incorrect voltage regulators used. Hence max voltage out of the alternator should be only 14.7 volts, and if the alternator is putting out higher than this, its the voltage regulator on the Alternator the problem.
Granted that the ECM controls the voltage of the alternator, but if the ECM has problems like feed back RF noise from the coils, then output of the alternator will be less than 14.7 volts only instead.
Granted that the ECM controls the voltage of the alternator, but if the ECM has problems like feed back RF noise from the coils, then output of the alternator will be less than 14.7 volts only instead.
Safety Car
Joined: Nov 2013
Posts: 3,554
Likes: 1,096
From: Ex DPRK, now just N of Medford, OR
Sorry to hear that the dealer used the shotgun approach to repairing your car.
They've probably been burned too often on charging system diagnosis.
The diagnostic procedure in the factory manual is WRONG... I followed it explicitly, it said I had a bad ECU. Nope, that wasn't it.
Turned out to be just a bad alternator. Compounding the confusion, the rebuilts I was getting had the wrong (C5) regulators, guaranteeing the svc chg system message.
Overcharging likely to be from bad regulator or bad ground.
Might be time to ditch the dealer in favor of an automotive electrical specialist. Nothing magic involved, despite GM's best efforts to confuse things.
I spent days going through my charging system issues, and found the service manual contradicts itself on the ECU's role in the charging circuit.
I suspect that it doesn't actually control it, but merely monitors voltage. The alternator charges just fine with the plug connector off...
Good luck, let us know how it comes out!
They've probably been burned too often on charging system diagnosis.
The diagnostic procedure in the factory manual is WRONG... I followed it explicitly, it said I had a bad ECU. Nope, that wasn't it.
Turned out to be just a bad alternator. Compounding the confusion, the rebuilts I was getting had the wrong (C5) regulators, guaranteeing the svc chg system message.
Overcharging likely to be from bad regulator or bad ground.
Might be time to ditch the dealer in favor of an automotive electrical specialist. Nothing magic involved, despite GM's best efforts to confuse things.
I spent days going through my charging system issues, and found the service manual contradicts itself on the ECU's role in the charging circuit.
I suspect that it doesn't actually control it, but merely monitors voltage. The alternator charges just fine with the plug connector off...
Good luck, let us know how it comes out!
