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Discussion Starter #1
Past few days my truck has been startin like the batteries r goin bad but I just figured it was the cold and I wasn’t waitin long enough to let the glow plugs up all the way. Last time I drove it was Friday. Today is Sunday and I tried to start the truck this mornin. DEAD. I drove work truck today and get home earlier and notice my parkin lights r on. But switch is off. WTH. Been a few years since I installed these batteries seems like. They r interstate batteries. But y is my parkin lights on with the batteries dead?
 

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Do you have any LEDs on the grid? (not just parks)
 

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Discussion Starter #3
No LEDs. Just factory lights and no accessory lights either. Only thing not factory electronically is that I have an inverter wired to the battery with an in-line fuse (bought the truck that way) it stays turned off.
 

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If you have one bad battery then you have two bad batteries. The way it works is like this:

When a battery dies it typically has a cell short out. This is usually because of a buildup of sulfate at the bottom of the cell but it can be from sulfate between the cells or some other cause. When the cell goes bad the battery becomes a 10.5 V unit. If the other battery is still good and has 12.6V then any time the engine isn't running the good battery will try to charge the bad battery. In other words the good battery will discharge through the bad battery until the voltage is the same in both. 10.5V is a really dead battery, normally. Running a starting battery, like we have in our trucks, down to that level will kill a good battery in short order.

If the good battery is still good, it will be dead whenever it comes time to crank the engine. Only the bad battery will have anything in it but it will be a 10.5V battery so it won't crank very fast and since it is now delivering twice the current it normally would the remaining 5 cells take a beating. Once this situation arises, the only fix is to replace both batteries. The exception would be if they were both fairly new and you caught the situation as soon as it happened. Otherwise you have a couple of anchors.

So what probably happened is that one battery went bad and started taking down the other, hence the bad starting. Now they are both bad.

You don't need glow plugs to get a Duramax to start in weather above 0F. Glow plugs are not your problem. In fact, letting them run may actually make it harder to start with weak batteries because the glow plugs will take a lot out of the batteries even before they get a chance to crank the engine. Not that I'm advocating not running the glow plugs normally. They make the engine run a lot smoother as it warms up and reduce stress on everything, including your ears.

Of course the real problem is the lights that don't shut off. Do you have a function on your truck that keeps the lights on for a minute or so to light the walk into the house?
 

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House walk function lights the DRLs and the backups on the rear, not the parks.
 
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I guess I could have looked it up but I'm lazy that way.

I don't know what they call it these days but it used to be called twilight sentinel on my parent's '65 Sedan De Ville. It looks like it would be "courtesy lamps". If that is so then it involves park/turn lamps, markers, clearance lamps, tail and license lamps. If all of these are on then the BCM is probably commanding the park lamp relay on for some reason.

You could scan the BCM and see what is going on but the likely cause is the door switches being stuck in the door open position. Ford used to have a big problem with this. As far as I know they still do. GM has decided they don't have enough of their own problems and has copied the Ford system to some extent.

I believe on the 2007 LBZ it requires replacing the whole latch mechanism if it is stick in the open position.
 

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I guess I could have looked it up but I'm lazy that way.
With the mods I've done to the two (fore/aft), it's quite the light show with the key fob at night. :howdy
 

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I don't know about 2007, but the LLY's have a problem with unsealed (on the top) batteries on the passenger side. Look to see if water from the cowl runs down onto the top of the passenger side battery. Water then seeps through the caps on top.

The solutions are to either (1) use batteries that don't have vents/caps on top, or (2) cover the top of the passenger side battery. I bought a battery case at Walmart, cut the top a little to clear the side terminals, plugged the vents it had, and strapped it on, discarded the rest of the battery box).

It turns out the gassers had an extra brace (I think you can see mounting holes) if they had the 2nd battery. The brace would direct water away. Diesels don't have that piece.
 

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Discussion Starter #9 (Edited)
Thanks everybody for y’all’s help. And Jake to answer ur question. I think mine does leak water on the pass side onto the batt. Cause I have a rust spot on my driveway kinda under where my pass side batt is. I’ve read somewhere that’s the cause of that. Never knew how to prevent it. Could that affect my batt life also? Btw got back from work tonite and the parkin lights r still on. Makes no sense y since the batt r dead.
 

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A battery that is too dead to crank the engine can still run lights.

You probably need to protect the battery from rain runoff because if it dilutes the electrolyte inside the battery it will ruin it but that has nothing to do with your lights staying on.

Try pulling the various lighting relays one at a time to see if that turns the lights off. You have about seven that could cause something like you are seeing but the main suspect is the park lamp relay. If that turns the lights off then try swapping a different relay into the same socket. If the lights come back on then the BCM is likely seeing something it shouldn't. If they don't come back on then you probably have a bad relay.

The rear defogger relay might be the same type of relay and would be a good test piece since you don't need the rear defog to get the truck to run.

Of course it is possible that you have a wire grounding out and keeping the park lamp relay turned on. You could unplug the BCM. It is mounted on the left side of the steering column under the dash. If unplugging it makes the lights go out then you probably have a door switch gone bad. If it doesn't then you probably have a grounded wire.
 

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Hey guys, is it possible the low voltage in the batteries has screwed with the BCM and caused it to not cycle the parking lights off as it should after some time when it was last shut off?

If so, a new set of batteries may in fact solve both issues?

but in the meantime pull Both negative battery cables to shut down the drain on them.
 

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Discussion Starter #12
Sry shoulda typed this up this mornin. But I got busy. I went outside to start the work truck this mornin and my park lights r off now. So could 407driver b right and now the lights r not on cause the batteries r completely dead?
 

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Sry shoulda typed this up this mornin. But I got busy. I went outside to start the work truck this mornin and my park lights r off now. So could 407driver b right and now the lights r not on cause the batteries r completely dead?
You know, it would be a lot more informative to just put a meter on the battery rather than ask someone many miles away what's going on.

When it comes to computers and low voltage, anything is possible. Many of the big computers in the truck, ECM, BCM, TCM, ICM, etc., need to shut down after a few minutes of waiting to see if you really want them to quit. If they don't have the proper voltage they can fail to go to sleep.

I would agree that the first thing to do here is to get good batteries into the truck. Perhaps the ones that are in it now would do but they need to be isolated from the truck, charged and then tested to be sure. This whole thing could be about bad batteries. There is no use in putting any more thought into the problems until there is a good baseline of battery power.

I'm done with random guessing. Get the batteries up to snuff and then test for current drains. That's the next thing to do.
 

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Discussion Starter #14
That’s my plan tomorrow. Thanks
 
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Past few days my truck has been startin like the batteries r goin bad but I just figured it was the cold and I wasn’t waitin long enough to let the glow plugs up all the way. Last time I drove it was Friday. Today is Sunday and I tried to start the truck this mornin. DEAD. I drove work truck today and get home earlier and notice my parkin lights r on. But switch is off. WTH. Been a few years since I installed these batteries seems like. They r interstate batteries. But y is my parkin lights on with the batteries dead?
my guess would be that with the battery voltage that low there is some kind of logic failure in the parking light switch or BCM that is activating the lights erroneously. These trucks do some really odd things when battery voltage drops below 10 volts, and ive seen some truly bizarre things when the voltage approaches 0. The logic circuits run at 5 volts but can work down to 2.5 ish. Below that and you may or may not have sufficient voltage to operate the logic circuit which can result in some random and unexpected behavior from the circuit.

I would put 2 new batteries in it and see if the issue goes away. If the batteries are dying over a weekend they need to be replaced, or you have a serious parasitic draw which i write a guide in this sub forum on how to troubleshoot.
 

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Discussion Starter #16
Update. Logical fix. Put new batteries n my truck yesterday evening and everything is good. (Woulda done it sooner but just didn’t have time). Fired right up. And to make it even better it only cost me $6 and some change. I run interstate. The old ones had 800 cca and the new ones have 850 cca and 1000 ca. They went bad within the 30 month free replacement warranty. When he tested the batteries each had bout 5-6 bolts on each of them. Just find it odd that they went bad so fast.
 

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I'm on my third set of batteries in my 2015. When one goes bad, it drags the other one down with it. The voltage can be fine, but the amperage is single digits.

It's almost like the truck should have a third, spare battery that isn't in the circuit, but can be switched on when needed.
 

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Update. Logical fix. Put new batteries n my truck yesterday evening and everything is good. (Woulda done it sooner but just didn’t have time). Fired right up. And to make it even better it only cost me $6 and some change. I run interstate. The old ones had 800 cca and the new ones have 850 cca and 1000 ca. They went bad within the 30 month free replacement warranty. When he tested the batteries each had bout 5-6 bolts on each of them. Just find it odd that they went bad so fast.
So I too recently had to replace two prematurely from autozone and they told me a few years ago they tried a “Summer” blend in the batteries that were sold in Texas that’s now proving to go bad early. I think the part number on the batteries had a “S” in it. Not sure if Interstate did the same thing or not.
 

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I'm on my third set of batteries in my 2015. When one goes bad, it drags the other one down with it. The voltage can be fine, but the amperage is single digits.

It's almost like the truck should have a third, spare battery that isn't in the circuit, but can be switched on when needed.
I was actually planning a summer project to add 2 frame mounted batteries on a dual 500 amp isolation solenoids as auxiliary batteries. They would all 4 be connected while the trucks running, but would be 2 isolated sets when the trucks off.
 

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I was actually planning a summer project to add 2 frame mounted batteries on a dual 500 amp isolation solenoids as auxiliary batteries. They would all 4 be connected while the trucks running, but would be 2 isolated sets when the trucks off.
With a dash mounted switch to activate the isolation solenoids for cranking when the mains are dead????

Sounds like something a guy with Ohm's law as his avatar would do.
 
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