low voltage at idle
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Joined: Dec 2013
Posts: 79
Likes: 10
From: Akron OH
I had a low voltage problem the beginning of summer, start up voltage would read 13.8 but after engine warm up would drop to 11.4 to 12.5 on DIC. Could not get the car into my regular dealer so I took it to the dealer I purchased it from ( non Chevrolet) expecting to replace the alternator good thing I have a warranty. Dealer could not find any problems with battery or alternator, after much research they found a GM service bulletin where for some reason the Gages would go out of sync ( I did not find out the reason) after they reset gauges have not had a problem since, voltage reads 14.6 to 13.8 under load.
Thread Starter
4th Gear
Joined: Aug 2016
Posts: 4
Likes: 1
From: Arrington TN
Low voltage C5
If you still have your original alternator, KEEP IT! Do not give it back as core. Plenty of horror stories here, just do a search on the subject.
C5s are very "picky" with alternators and when these are not replaced with the right ones, it causes charging system fault codes.
When your car is showing low voltage, have you checked what voltage you have between the alternator and the battery's positive post? It should be zero or very, very close to it. If it is significant, you probably have a bad contact at the starter or a bad fusible link. The chain is alternator-starter-battery.
C5s are very "picky" with alternators and when these are not replaced with the right ones, it causes charging system fault codes.
When your car is showing low voltage, have you checked what voltage you have between the alternator and the battery's positive post? It should be zero or very, very close to it. If it is significant, you probably have a bad contact at the starter or a bad fusible link. The chain is alternator-starter-battery.
Melting Slicks
Joined: Jul 2015
Posts: 2,297
Likes: 232
From: Round Rock Texas
9-10-16 update: Ok i revcieved my replacement voltage regulator M530 on 9-6-16. Installed it into my GM original altenator and placed it onto the vette. Well i have not notice much improvment than before. The vlotage still drops to 12.9 at idle with AC and head lights on and the car is at temp. When car is cold I read 14.1v with AC and lights on. I can tell the gages seams to be close because the AC fan motor will change speeds when the voltage drops to 11.9. Now I can speed the idle (with my foot) and the voltage will climb. At speeds above 30, I read about 13.3 to 13.6v. for now I will just keep driving it to see if things improve. The voltage between the + battery and the + on the altenator to ground both read 12.3v. The voltage read between the + on the battery and the + on the altnator is zero.
on the altenator to ground both read 12.3v
Check what you get with car off at battery. If it is the same bad battery. Someone will post the bad voltage levels
Drifting
Joined: Jul 2015
Posts: 1,844
Likes: 375
From: San Jose, CA
Disagree, sirdano. Usually, even a moderately bad battery won't prevent the alternator output from being high. We know this because a good battery with, say, 12.7v, will still allow the alternator to put out a solid 14v. A battery is a complicated chemical device and doesn't simply limit the applied voltage across its terminals to its generating voltage.
However, if the alternator has been running at 12.3v, which is below good battery charge level, the battery will have slowly discharged until its internal voltage (chemical driven) was 12.3v - that is, pretty discharged.
The better test would be to turn the car off, hook up the battery to a battery tender, then the next day, turn off the tender, and check to see if the battery is properly charged up. A proper load test would be even better.
However, if the alternator has been running at 12.3v, which is below good battery charge level, the battery will have slowly discharged until its internal voltage (chemical driven) was 12.3v - that is, pretty discharged.
The better test would be to turn the car off, hook up the battery to a battery tender, then the next day, turn off the tender, and check to see if the battery is properly charged up. A proper load test would be even better.
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Melting Slicks
Joined: Jul 2015
Posts: 2,297
Likes: 232
From: Round Rock Texas
Disagree, sirdano. Usually, even a moderately bad battery won't prevent the alternator output from being high. We know this because a good battery with, say, 12.7v, will still allow the alternator to put out a solid 14v. A battery is a complicated chemical device and doesn't simply limit the applied voltage across its terminals to its generating voltage.
However, if the alternator has been running at 12.3v, which is below good battery charge level, the battery will have slowly discharged until its internal voltage (chemical driven) was 12.3v - that is, pretty discharged.
The better test would be to turn the car off, hook up the battery to a battery tender, then the next day, turn off the tender, and check to see if the battery is properly charged up. A proper load test would be even better.
However, if the alternator has been running at 12.3v, which is below good battery charge level, the battery will have slowly discharged until its internal voltage (chemical driven) was 12.3v - that is, pretty discharged.
The better test would be to turn the car off, hook up the battery to a battery tender, then the next day, turn off the tender, and check to see if the battery is properly charged up. A proper load test would be even better.
12-30-2012, 01:15 PM #8
AlfredMay
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As stated by the gentleman from the Cumberland Plateau.... a new battery should register 12.8 volts when not being charged. The older it gets the lower the voltage will be. The chart below shows that your battery is dead It could also be that your volt meter is off....... or your battery still has a parasitic draw. None of this is good news.
State of Charge Specific Gravity Voltage
12V 6V
100% 1.265 12.7 6.3
75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Discharged 1.120 11.9 6.0
Melting Slicks
Joined: Jan 2009
Posts: 3,275
Likes: 739
From: Miami FL
This test requires that measurements are taken with the engine running and, in your case, when it is at operating temperature, idling and showing low voltage.
Last edited by GCG; Sep 11, 2016 at 07:15 PM.