C5 Dead Battery Again
Thread Starter
Burning Brakes
Joined: Jun 2007
Posts: 757
Likes: 13
From: Norfolk VA
C5 Dead Battery Again
After replacing the battery and alternator two weeks later I have a dead battery. Used jump box and alternator gauge showing consistent 3.5 - 3.8V. What else do I need to look at?
Melting Slicks
Joined: Nov 2014
Posts: 3,399
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From: Havre de Grace Maryland
A thought, if you are not into electrical problem sorting out, consider getting a cut off switch at the negative battery terminal. Not a fix, but it does stop the parasitic drain until someone can figure it out for you.
Race Director
Joined: Jul 2008
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From: The Sunshine State
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Did you install any aftermarket electronics such as a new audio system or sub-woofer?
Le Mans Master
Joined: Feb 2021
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From: Florida
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Excellent video to help you isolate to drawing circuit.
Ps. Remember to check the passenger footwell fuses too.
Ps. Remember to check the passenger footwell fuses too.
Race Director
Joined: Oct 2004
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When my car took a brand new battery down to zero in 24 hours, it was my BCM. I've also heard that a bad seat control module can do this. There's a nice little unit called, IIRC, "Priority Start." It kills power to the car at around 11.5v, give or take, saving what is left to start the car. Good luck..... 
Last edited by grinder11; Aug 18, 2022 at 08:19 AM.
Le Mans Master
Joined: Feb 2021
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From: Florida
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When my car took a brand new battery down to zero in 24 hours, it was my BCM. I've also heard that a bad seat control module can do this. There's a nice little unit called, IIRC, "Priority Start." It kills power to the car at around 11.5v, give or take, saving what is left to start the car. Good luck.....
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Le Mans Master
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From: Virginia
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St. Jude Donor '21-'22
You definitely have parasitic loss going on. You could hook the battery up to a charger while you try to track it down. A good charger is a wothwhile investment to keep your battery lasting longer even after you find and fix the issue. Good luck.
Race Director
Joined: Oct 2004
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I don't post any pics, because I've never taken the time to really learn. Poor excuse, I know. I fixed what was wrong with my car, and removed it. Its a yellowish, mustard colored plastic piece, and I believe it is branded "Priority Start". I no longer use it, because I have performance mods, and a custom tune. I think that the PCM has to re-learn some functions when the PS disconnects the car from the battery. I don't honestly remember. Anyway, if that is the case, a stock engine will idle fine after the disconnect, but one with a performance cam (like mine) may take a couple weeks to start behaving again. If you want one, I haven't really thought about selling mine, but I probably should, because all it does is take up shelf space in my garage. Looking up priority start for c5 corvette. It shows a pic of what I have. I see they're going for $110.00+ new. I'd take $60 shipped.........
Le Mans Master
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@grinder11
Hmmm. I’ll be installing a cam, getting a tune, etc this fall. If the custom tune is an issue….
Funny thing, too. I found it odd that this device disconnects on the hot side instead of the ground. It’s been so long I don’t remember which leg was used on my racing kill switch.
Hmmm. I’ll be installing a cam, getting a tune, etc this fall. If the custom tune is an issue….
Funny thing, too. I found it odd that this device disconnects on the hot side instead of the ground. It’s been so long I don’t remember which leg was used on my racing kill switch.
Melting Slicks
Joined: Jun 2013
Posts: 3,473
Likes: 691
From: West Virginia
I don't post any pics, because I've never taken the time to really learn. Poor excuse, I know. I fixed what was wrong with my car, and removed it. Its a yellowish, mustard colored plastic piece, and I believe it is branded "Priority Start". I no longer use it, because I have performance mods, and a custom tune. I think that the PCM has to re-learn some functions when the PS disconnects the car from the battery. I don't honestly remember. Anyway, if that is the case, a stock engine will idle fine after the disconnect, but one with a performance cam (like mine) may take a couple weeks to start behaving again. If you want one, I haven't really thought about selling mine, but I probably should, because all it does is take up shelf space in my garage. Looking up priority start for c5 corvette. It shows a pic of what I have. I see they're going for $110.00+ new. I'd take $60 shipped.........
Race Director
Joined: Oct 2004
Posts: 12,864
Likes: 4,669
@grinder11
Hmmm. I’ll be installing a cam, getting a tune, etc this fall. If the custom tune is an issue….
Funny thing, too. I found it odd that this device disconnects on the hot side instead of the ground. It’s been so long I don’t remember which leg was used on my racing kill switch.
Hmmm. I’ll be installing a cam, getting a tune, etc this fall. If the custom tune is an issue….
Funny thing, too. I found it odd that this device disconnects on the hot side instead of the ground. It’s been so long I don’t remember which leg was used on my racing kill switch.
Safety Car
Joined: Aug 2008
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From: Red city in deep blue Oregon
St. Jude Donor '17
When my car took a brand new battery down to zero in 24 hours, it was my BCM. I've also heard that a bad seat control module can do this. There's a nice little unit called, IIRC, "Priority Start." It kills power to the car at around 11.5v, give or take, saving what is left to start the car. Good luck.....