Need Help with Parasitic Drain Test C5
Thread Starter
Joined: Jan 2025
Posts: 11
Likes: 1
From: Tampa
Need Help with Parasitic Drain Test C5
Hey everyone! Today, I conducted a parasitic drain test on my 2003 C5 Corvette. My battery has been dying over night and has a hard time starting in the morning but it will eventually crank if i keep holding the key to the right lol. The battery voltage will be around 9.2v in the morning when i wake up. So today I disconnected the negative battery terminal and used a multimeter to measure the current draw. I found a reading of 1.30 amps, which is significantly higher than the normal parasitic draw for this model. I tried removing most of the fuses, but that didn't reduce the draw much, except for the BCM1 + IPC #25 fuse, which dropped the draw by about 0.40 amps. However, there's still a 0.90 amp draw from somewhere else.
I also recorded a video where, when connecting the multimeter to the battery, I could hear a clicking or motor-like sound, similar to what you'd hear when trying to start a car with a dead or dying battery. I suspect it might be related to the ignition switch or starter, so I checked the ignition switch by disconnecting its wiring harness and cleaning the contacts. Even with the ignition switch disconnected, there was still a draw. Not sure what could be causing this. Maybe something with the starter? The car cranks right up if the battery is charged above 11v though. Any experienced electrical c5 guys willing to help me figure this out? Thanks
Here is the video:
I also recorded a video where, when connecting the multimeter to the battery, I could hear a clicking or motor-like sound, similar to what you'd hear when trying to start a car with a dead or dying battery. I suspect it might be related to the ignition switch or starter, so I checked the ignition switch by disconnecting its wiring harness and cleaning the contacts. Even with the ignition switch disconnected, there was still a draw. Not sure what could be causing this. Maybe something with the starter? The car cranks right up if the battery is charged above 11v though. Any experienced electrical c5 guys willing to help me figure this out? Thanks
Here is the video:
Last edited by SchlapC5; Jan 22, 2025 at 07:24 PM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,627
Likes: 4,071
From: Cape Coral, Florida
Pulling fuses isn’t the best way to do a current draw test…you should see about 25 milliamps max…watch the videos and make sure the battery is fully charged first…a bad diode in the alternator can cause a draw…disconnect the alternator B+ to check…you can split the electrical system in 2 by disconnecting the underhood fusebox B+ and check for draw.
Thread Starter
Joined: Jan 2025
Posts: 11
Likes: 1
From: Tampa
Ok ill check the alternator B+ soon! I was trying to check the fuses using the multimeter but i have one of those cheap ones from harbor freight & wasn't getting any readings on the screen. No matter what setting i tried.
Le Mans Master
Joined: Jul 2002
Posts: 7,370
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From: Slave to the evil empire
Cruise-In V Veteran
St. Jude Donor '04
Last year I had the same problem, it turned out to be the drivers side seat controller. I sat in the car and waited for everything to shut down, then I could hear a slight whine sound, turned out to be the seat motor.
Melting Slicks
Joined: Sep 2008
Posts: 3,138
Likes: 802
From: Espanola New Mexico
To the OP, the clicking sound you hear when connecting meter leads to measure current drain is the headlight control module, this will happen when you connect the negative battery cable back on, this is normal. As previously mentioned you can isolate the electrical system by lifting the positive battery cable at the engine fuse box, this will leave the starter and alternator as the only things connected to the battery. By lifting the positive battery cable that powers the interior fuse box you can isolate the fuse box's, that cable is located in the engine fuse box. Good luck.
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Thread Starter
Joined: Jan 2025
Posts: 11
Likes: 1
From: Tampa
Thank you yall for the great responses! I disconnected the B+ from the alternator as well as the other electrical cable attached to it. Still has the draw, so not the alternator. Gonna try again soon but using the fuse box split like yall are saying to help finding the problem faster!
Advanced
Joined: Sep 2024
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From: Oulu, Finland
2025 C5 of the Year Finalist - Modified
My draw was the co pilot seat, motor or switch I dunno but just disconnecting the wiring from switch cured my draw issue. Found many similar stories here when hunting down the problem.