Hi all.
Need some real help with this one. I'm usually pretty good at this stuff but this one is killing me. Iv have been having this electrical issue. Something is draining my battery, maybe a short maybe an open ground, I don't know. The timeline has been, it used to be car would not start randomly, then i said ehh maybe lights or something like a dope. ill just jump it. Then it would be fine for a while. Then it would do it again. so ok maybe my brain is off and i did it again. jumped it. fine for a little . 3rd time down the road i said ooook maybe something in the fuse panel is being supid, after i pulled all the fuses and found nothing. Then i replaced the fuse panel. Happened again month or so later. now lets go for the obvious and go for the battery. Changed the battery. Then fine for about 3 months. Then i returned the battery "battery was bad" got a new one. Then i noticed volts would go the 14.9 then back to low 12s. for a little. Then i put the volt meter inline and pulled fuses to find an amp draw. didnt find anything (if i didt cause the computers or ii second guessed something). ok maybe alternator. Changed it. then at that same time, I pulled every single fuse out and worked backwards, putting fuses in, try something different. What i thought was the onstar that was drawing, i left the fuse out cause i dont use it. Hurray i thought i got it finally. last week, same thing. no start.
Now the other troubleshooting things. now interesting thing is that car will sit at 12v ish. once i put it in the on, not start, voltage starts goin down. I left the meter on it
I checked sanded and dielectric greases the from driver and passenger ground under the fog lights, same with the ground on the frame under the driver door. Iv already upgrades the battery to frame ground and battery to engine ground a while back. Now desprate move, i got one of those AutoStart things, that turns off when it sees a draw... I put the trickle charger on it, got the battery to 12v, when i go in the truck and enguage the auto start, the battery drops down to 10 volts without me even doing anything, which makes sence why the truck doesnt start.
My question is, can you guys start throwing things at me to try other then what i did already? Other grounds, other dumb things who knows. Anythng would help

Dan O

2008 H2

 

is the onstar functional? does it have aftermarket alarm or remote start?

 

I never used it. I pulled the fuse out and left it when I thought that was it. It has an alarm but I believe it's the stock one. I have never had a key fob for it. There is something going on with a switch that looks like the privous owner did with 2 other relays. But I turned that switch off and disconnected the relays. I still need to trace it and see what it is. It's under the stearing colum
Dan

 

Couple of suggestions.

• Invest in a battery tester, this will indicate the battery's State Of Health (SOH) State of Charge (SOC) plus Alternator Charging and cranking amps, the technology is amazing, a multimeter will only provides a little part of the story.
• Lead acid batteries do bode well under pre-longed low volts, if the engine struggles to start either charge the battery or disconnect it. Try to keep the battery used and charged. Not all new batteries are 100% healthy as I found out
• Check the parasitic drain. Connect a 1ohm 10Watt resistor in the negative lead so1mV = 1mA . It make take some time for the BCM etc to go quiet, so give it an hour to settle. According to GM the parasitic current drain should be around 30mA.
• Watch this video

I can't get mine below 38mA no matter how many fuses I pull.

The data below came from GM, its current vs time for the battery to drop to 50% charge.

 

ok thanK You. Went threw 2 yellow too agm batteries. When the battery is disconnected from the fuse boxes, it will charge with the trickle charger to 12 pluss volts, only the fuse panel feed line is connected to the battery, the battery goes right to 10volts. Without even cranking it. Just right when the fuses boxes are connected.
I Will try those next though

 

I'd try a regular flooded lead acid battery too if your Optima is going bad...... Optima quality went in the toilet years ago. I've also tried two different newer AGM batteries in the past 4 years on other vehicles and neither one lasted more than a year and half.

 

It could also be something like a stuck relay. A 12 to 10 volt drop is a lot when connecting it. Do yourself a favor and go to a hardware or auto parts store and get a multimeter that does DC amps. Make sure it’s rated for at least 10 amps and be sure you read the instructions as amp testing often uses different plugs on the meter vs voltage testing.

next connect the battery in series with the amp meter and start pulling fuses and relays until you see the amperage decrease. be sure you have all headlights, parking lights, and interior lights off as well as the keys out of the ignition because this could be too much current and fry the meter. Remember there are fuses inside the truck for the dic too.

If it still draws more than like 100ma after sitting for an hour with all fuses and relays out, try unplugging the ecu connectors. I wouldn’t expect this to be an issue with the fuses removed but hey, who knows what goes on in these fancy spider web wiring harnesses.

one last thing. Make sure there are no extra cables tied directly to the battery lugs. There should only be 1 negative and 1 maybe two positive wires going to the battery.

 

Funny thing is actually I ordered a DC amp meter yesterday. That was going to be my next step.
My multi meter I have only goes up to 5 amps. When I put it in series with the neg terminal before, it was too much for it. Hopefully once I get that thing in and pull fuses again. I have a direction to go.

 

Just watched a video on YouTube. There was corrosion on the underside of his fuse box under the hood. A little bit different problem depending on how much corrosion I suppose.he pulled it out and cleaned the pins and he was gtg. Ya never know.

 

Aaaaaaaaa. I have the fuse box apart too. Can you send me that video please