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Battery drains within a day of turning off the truck?

Tiny
PWRDRAINSILVERADO
  • MEMBER
  • 2000 CHEVROLET SILVERADO
  • 4.8L
  • V8
  • 4WD
  • MANUAL
  • 58,000 MILES
Battery goes dead within a day of turning off the truck and removing the key. It has a new battery because I thought the original battery just went bad but there is definitely a draw.

I keep the negative cable unhooked. When I hook up the cable, the amp draw drops to 0.003 amps in 2mins and 15 secs. I believe this is probably normal.

If I open a door or turn on the dome light or cargo lamp and then turn it off, the draw never goes down to.003 amps. It stays at approximately 0.185 amps forever. The lights go out.

I can reset it by disconnecting the negative battery cable or removing and re-inserting the TBC fuse.

I have already replaced the BCM, headlight switch module (OEM) and relays to the courtesy lighting circuit.

Everything works on the truck as far as I can tell.

I have back probed the BCM connectors but I'm not sure what to do with that info.

I thought by now I would have found the problem but haven't. Any help is appreciated.
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Monday, September 9th, 2024 AT 3:21 PM

16 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

When you get the larger draw, at that point, remove one fuse at a time in the under-hood fuse box. When the draw drops back to .003 amps (3 milliamps), we will have narrowed down a circuit. Normal amperage draw should stay between 50 and 75 milliamps. 0.185 amps = 185 milliamps which is way too high.

Try this and let me know what you find. Once this is done, I can check to see what all a specific fuse powers for you. At that point, we will simply disconnect one component at a time to see which one is causing the draw. Keep in mind, this could be coming from several different areas. For example, an alternator with a faulty diode can back feed power or even an electric seat. Take a look through this link to see if anything helps:

https://www.2carpros.com/articles/car-battery-dead-overnight

Let me know.

Joe
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Monday, September 9th, 2024 AT 7:56 PM
Tiny
PWRDRAINSILVERADO
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The draw goes to 0.003 when I pull the TBC fuse. There is also a draw on the ctsy fuse but only drops to.068 when it’s out by itself. I put it back in and pulled the TBC fuse and it goes to 0.003.
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Tuesday, September 10th, 2024 AT 5:19 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
That fuse is for the body control module. Here is what to do next: On the lower left side of the IP below the steering column is where it is located. See pic below.

Disconnect it to see what happens with the voltage. If there is no change, the problem is in either the wiring or the connector. If it drops, suspect the BCM is shorted internally.

Let me know.

Joe

See pic below.
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Tuesday, September 10th, 2024 AT 6:20 PM
Tiny
PWRDRAINSILVERADO
  • MEMBER
  • 9 POSTS
There are 3 connectors that go into the BCM: 1) the right connector is purple and made no change to the draw when removed; 2) the middle connector is lite blue and made no change to the draw when removed; and 3) the left connector is brown and dropped the draw to 0.003 when removed.

I back probed the brown connector with the draw active and found voltage on the top connector pins (3, 10 and 12). These have no voltage present when there was no draw.

Can you see what the pinout is for the brown connector and pins?

Thanks

I have already replaced the BCM prior to contacting you and I still have the same problem.
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Wednesday, September 11th, 2024 AT 10:53 AM
Tiny
JACOBANDNICKOLAS
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Hi,

The two rows of connector pins are identified as A and B. The pins are A1 to A12 and on the bottom, B1 to B12.

I'm not sure which you are referring to, so I attached the connector pin layout along with what each pin is for.

Let me know if this helps.

Take care,

Joe

See pics below.
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Wednesday, September 11th, 2024 AT 6:24 PM
Tiny
PWRDRAINSILVERADO
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This is nice information to have.

The connectors with voltage with the draw active are B3, B10, and B12. I thought B10 was going to help because that is the parking brake switch. I unhooked the lead at the parking brake switch (goes to B10) and there is no change.

B12 goes to tow/haul mode but the truck has a manual transmission so there is no tow/haul mode.

This truck has manual windows, manual door locks and manual mirrors. It is a very plain model. The only luxury is air conditioning and a factory am/fm radio with cassette player.

I also tested the original BCM again and got the same results as with the replacement BCM.

I'm out of ideas. The best I can get the draw is to 0.067 amps with the CTSY fuse pulled (other than pulling the TBC fuse). I think 0.067 amps is at the upper end of the acceptable draw range.

Maybe I'll try leaving the CTSY fuse out and see how long the battery lasts. But the battery is already weakened from going dead and I don't want to hurt it anymore.

Thanks for the help.
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Thursday, September 12th, 2024 AT 8:58 AM
Tiny
JACOBANDNICKOLAS
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Hi,

B2 is a voltage reference feed. Do me a favor. Disconnect the connector on the 4wd shift motor on the transfer case and see if the voltage drops.

Also, I attached diagnostics below for a parasitic draw. Take a look through them and maybe we missed something.

Let me know.

Joe

See pics below.
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Thursday, September 12th, 2024 AT 7:53 PM
Tiny
PWRDRAINSILVERADO
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My truck has a manual lever to switch the transfer case. I don't believe it has a 4wd shift motor.

I don't have the parasitic test tool but I connect my multimeter inline as it describes to measure overall amperage draw. My meter goes up to 20 amps.
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Friday, September 13th, 2024 AT 8:35 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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If you have a 20-amp draw, I'm surprised something hasn't melted down. Do you mean amps and not milliamps, correct?

As far as the CTSY fuse, that powers the inadvertent power relay. This relay is what powers things when the key is in the off position, and it is located in the interior fuse panel under the dash.

I attached a pic below showing the relay location. Remove it and let me know what happens to the draw.

Joe

See pic below.
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Friday, September 13th, 2024 AT 8:55 PM
Tiny
PWRDRAINSILVERADO
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With the inadvertent relay pulled, this is what happens:
I connect the negative battery cable and 2 mins 15 secs later the draw settles to 0.003 amps. When I open the driver's door, the draw initially goes to 0.528 amps then settles to 0.110 amps in about 15 seconds. When I close the door, the draw stays at 0.110 amps for a few seconds then settles down at 0.067 amps and stays there.

With the inadvertent relay in, this is what happens:
I connect the negative battery cable and 2 mins and 15 secs later the draw settles to 0.003 amps. When I open the driver's door, the draw initially goes to 2.058 amps then settles to 1.665 amps in about 15 seconds. When I close the door, the draw stays at 1.665 for a few seconds then settles down at 0.184 amps and stays there.
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Saturday, September 14th, 2024 AT 5:47 PM
Tiny
JACOBANDNICKOLAS
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Hi,

Okay. We still aren't too far off. I have one more test for you. Carefully disconnect the power at the alternator and see if it drops. We could have a diode allowing power to back feed to ground. I'm sure you already know this, but battery voltage is always present at the alternator. Make sure not to allow the connectors to short.

Let me know.

Joe
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Sunday, September 15th, 2024 AT 7:16 PM
Tiny
PWRDRAINSILVERADO
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No change with alternator unplugged. The draw is still 184 milliamps.
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Monday, September 16th, 2024 AT 4:37 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

At this point, the only thing I can suggest is to scan the can-bus system to see if there is anything stored as far as code, specifically related to the body control module. I realize it is new and has the same readings as the original one, but that is the last link I can think of.

Here is a link explaining how to scan the CAN:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

If this is something you have already done, let me know.

Take care,

Joe
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Monday, September 16th, 2024 AT 8:42 PM
Tiny
PWRDRAINSILVERADO
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I had to order a scan tool. I should have it in a few days. I’ll let you know what it says.
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Tuesday, September 17th, 2024 AT 2:36 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Sounds like a plan. Let me know what you find.

Take care,

Joe
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Tuesday, September 17th, 2024 AT 7:58 PM
Tiny
PWRDRAINSILVERADO
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I scanned it and there are no codes.

At this point, I’m not going to work on it anymore. I have tried everything and spent $400 and made no progress. I can just hookup the battery cable each time I want to run the truck.

Sorry for the trouble and thanks for your help.
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Friday, September 20th, 2024 AT 4:30 PM

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