Battery voltage too low?
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2025 C4 of the Year Finalist - Modified
Battery voltage too low?
Car has a new battery as of January 2018. Duralast gold.
So on a cold start, voltage will read 14.5-14.7 volts. That seems good to me. But when the engine is warm and the AC is on, I have seen the voltage go as low as 12.6-12.4 at a stop light. Only goes that low stopped in drive. This is all via the DIC.
93 lt1
So on a cold start, voltage will read 14.5-14.7 volts. That seems good to me. But when the engine is warm and the AC is on, I have seen the voltage go as low as 12.6-12.4 at a stop light. Only goes that low stopped in drive. This is all via the DIC.
93 lt1
Le Mans Master
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From: Communist Colorado
Cold start seems good to me. The 12.4 is still a fully charged battery. At a stop light, both fans running, foot on brake (lights),radio probably playing, maybe a turn signal on.... plus the addition of the A/C compressor drag... I think youre ok.
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From: Dallas Texas
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Thanks guys. Reason why I am concerned is because with AC on, and the voltage goes to 12.4 or 12.6, the cooling fans are less noisy and the signal light blinks slower.
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Thread Starter
Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Gonna take me a while decipher that^. But thank you. I know the 4 pin connector is under the alternator. Is there a way to determine if the alternator itself is bad?
Also, do I run those tests with the car running?
Also, do I run those tests with the car running?
Last edited by 1993C4LT1; Aug 9, 2018 at 05:38 PM.
Le Mans Master
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From: Communist Colorado
A very basic test is to turn every accessory on... every one... Take a volt meter and check the voltage at the battery terminals. Should be 14.4 to 14.7 If its more than a volt under that, then your alternator is probably not outputting what it should be.
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Awesome, thank you sir. So should it be putting that voltage on a cold or hot engine? Of course, I'll run the test with all accessories on.
Le Mans Master
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From: Communist Colorado
. I would imagine a fully warmed up engine would be a better way to test..... When its cold there will be a voltage spike from the demand that was just placed on the battery to start the engine... without any-accessories on, it should very soon settle down to 13.4 to 13.7 ish...
So remember also, that you need to have all the basics covered as well..... all connections are tight, both pos and neg cables (at the starter also) are tight, clean and free of corrosion. You may get lucky and find that its a loose or dirty battery cable connection...
Another thing you can do is just remove the alternator and take it to an Autozone or the like and have them test it out....
So remember also, that you need to have all the basics covered as well..... all connections are tight, both pos and neg cables (at the starter also) are tight, clean and free of corrosion. You may get lucky and find that its a loose or dirty battery cable connection...
Another thing you can do is just remove the alternator and take it to an Autozone or the like and have them test it out....
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I don't get what you are saying. Are you saying my voltage drop is "within spec"?
Last edited by 1993C4LT1; Aug 10, 2018 at 10:43 AM.
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Hes not saying something important as it relates to your particular issue.
Go do what 81c3 said to do and report back what the voltage is.
Last edited by PatternDayTrader; Aug 10, 2018 at 05:58 PM.
Melting Slicks
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From: Mystic CT
I am saying that the gauge of the wire and distance run will be hard pressed to supply the current needed at 13.7 volts. On a '91 it does not look much larger than 10 gauge and no way to pass the current from 2 fan motors a/c clutch and blower motor plus no doubt radio. Just add the loads up along with current capacity of the wire. The other thing is to put a tach on the engine and see if it is really at 650 to 700 rpm as C4 tachs are notorious for reading wrong and usually high.
Le Mans Master
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From: Las Vegas - Just stop perpetuating myths please.
Car has a new battery as of January 2018. Duralast gold.
So on a cold start, voltage will read 14.5-14.7 volts. That seems good to me. But when the engine is warm and the AC is on, I have seen the voltage go as low as 12.6-12.4 at a stop light. Only goes that low stopped in drive. This is all via the DIC.
93 lt1
So on a cold start, voltage will read 14.5-14.7 volts. That seems good to me. But when the engine is warm and the AC is on, I have seen the voltage go as low as 12.6-12.4 at a stop light. Only goes that low stopped in drive. This is all via the DIC.
93 lt1
Thread Starter
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
So this is weird. I had my mom sit in the car with the car in gear, idling all accessories on. LCD was showing 12.6v but my multi meter was saying 12.09v. Told her to put it back in Park, and the LCD showed 13.6. Looked at my meter and it was showing the same. Either way, I have to test it more to see if the meter gives a consistent 12.09v reading. Right before I started to get the ramps out(to get under the car) it started storming.