Id bring the battery too and have it load tested while you're there.
Battery voltage too low?
Melting Slicks
Joined: Nov 2013
Posts: 3,451
Likes: 336
From: Greater Cincinnati Area.
That is a little low. Check your connections, including engine ground.. The large wire on the post at the back of the alternator does the charging. It should be clean and relatively tight. Voltage went up because it was spinning faster in park.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
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From: Mystic CT
I just did a computation for resistance of a 6 foot section of 10 gauge wire. .01 ohms. That is .5 volt at 50 amps. The CS alternator systems output wire and a sense wire go to the junction stud behind the battery. All the major loads are taken off this stud. The regulator will command the alternator output voltage to be what ever it needs to be to have "set voltage" at the sense wire input. So if the set voltage is 14.0, and there is 50 amps of load on the junction, the output voltage at the alternator will be 14.5 to cover the half- volt drop in the wire between the stud and alternator output. GM has done it this way for about 50 years. It works because the load is never equivalent to alternator output, and the wire gauge will current-limit the output anyway.
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
So I checked all connections for tightness and cleanliness. All looks good to me. I made sure with wrenches to see if it was tight, everything is. Pics in case you guys see something bad.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
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From: Las Vegas - Just stop perpetuating myths please.
FYI you can measure the resistance across each connection to verify good continuity. Good connection should be less than 2 ohms. Also you can measure the voltage drop across each connection but that maybe difficult in hot/tight areas but voltage drop should be less than 0.2 volts. Finally you can measure the full resistance from alternator to battery positive but you may need longer meter leads for this. Same goes for total voltage drop to battery positive.
This maybe helpful if you suspect poor connections.
Have you compared your in car/dash volt meter to a good quality hand held meter at the wiring diagrams connection point for the dash meter?
This maybe helpful if you suspect poor connections.
Have you compared your in car/dash volt meter to a good quality hand held meter at the wiring diagrams connection point for the dash meter?
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
FYI you can measure the resistance across each connection to verify good continuity. Good connection should be less than 2 ohms. Also you can measure the voltage drop across each connection but that maybe difficult in hot/tight areas but voltage drop should be less than 0.2 volts. Finally you can measure the full resistance from alternator to battery positive but you may need longer meter leads for this. Same goes for total voltage drop to battery positive.
This maybe helpful if you suspect poor connections.
Have you compared your in car/dash volt meter to a good quality hand held meter at the wiring diagrams connection point for the dash meter?
This maybe helpful if you suspect poor connections.
Have you compared your in car/dash volt meter to a good quality hand held meter at the wiring diagrams connection point for the dash meter?
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Battery is bought new back in January of this year. Still worth getting it tested? But yeah, the alternator is easy to take off. I have no problem with that.
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Le Mans Master
Joined: Dec 2005
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From: Communist Colorado
In my humble opinion, yes. Ya just never know and if they both test fine, you can start looking at other parts of the system. Sometimes battery cables, though look good, are corroded under the jacket... especially near the connection points. The positive cable looks like maybe it would be worth removing for a check. A sign of internal corrosion can sometimes be seen by the jacket "swelling" a bit. Im not saying any of this is definitively your problem, just might be things to consider.
Thread Starter
Race Director
Joined: Oct 2011
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Very true. One thing I forgot to mention, the voltage only goes to 12.6 volts with all accesories on, warm engine, at idle in gear. Driving, voltage is fine. Would a bad alternator have low voltage at all times?
Race Director
Joined: Oct 2008
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From: Lansing MI
Are you experiencing any symptoms besides the low voltage indication ?
Race Director
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From: Lansing MI
Ive seen things like what you have described but it was always accompanied by other symptoms.
For example, a screwed up power seat switch may not move the seat, but it may sit there cycling the circuit breaker, and as it draws 20 amps or so, system voltage may drop into the twelves. But, you have a dead battery in about an hour after you shut the car off.
For example, a screwed up power seat switch may not move the seat, but it may sit there cycling the circuit breaker, and as it draws 20 amps or so, system voltage may drop into the twelves. But, you have a dead battery in about an hour after you shut the car off.
Thread Starter
Race Director
Joined: Oct 2011
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Just the signal starts blinking slower, and when the voltage goes to 12.6, the fans are less audible. I just took the car for a drive to get the temp warm. Got home, AC on, all lights on even hazards. Engine in Park. Multimeter black probe on negative post of the battery, and positive on the alternator post. It went 12.8 volts, but of course it will go lower with the car in gear. I can't get a voltage reading in gear because I am by myself.
Race Director
Joined: Oct 2008
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From: Lansing MI
Just the signal starts blinking slower, and when the voltage goes to 12.6, the fans are less audible. I just took the car for a drive to get the temp warm. Got home, AC on, all lights on even hazards. Engine in Park. Multimeter black probe on negative post of the battery, and positive on the alternator post. It went 12.8 volts, but of course it will go lower with the car in gear. I can't get a voltage reading in gear because I am by myself.
All things considered, it sounds like you either have an alternator problem brewing or there's nothing wrong.
I would keep my voltmeter in the car and put some more miles on it.