Two Batteries- Parked for 6 days - Dead

[Awfiretto]

Quick post - just got back from a flight - frustrated -

2 months ago, 5 year old battery died - I installed (parallel) 2 brand new batteries.

Parked for a week - truck was dead? Charging levels are right

What’s the creep? BCM is what I read most common?? Any other quick suggestions or experiences?

Thanks in advance

 

[swathdiver]

Gotta use bi-directional scan tool and see how much parasitic draw it has. Could be any number of things.

 

[iamdub]

Or a digital voltmeter that reads amperes ("amps") and test each circuit individually. A $5 (or free) Cen-Tech DVOM from Harbor Freight will be sufficient for this.

Just one of many how-to videos:

 

[Doubeleive]

normally I would say you left something on, or something was plugged in and drained it from a power socket. otherwise you might have to trace it down by disconnecting the battery ground and put a electric meter between the battery terminal and the ground post and check what the draw is, then starting pulling fuses until you find the source.

 

[intheburbs]

Going forward, maybe install a battery isolator to prevent future deadness? Both of my trucks have dual batteries, and I did the install using factory TP2 parts, which include an isolator tied to the ignition, so it engages automatically.

 

[Awfiretto]

Thanks all!

Battery isolator will be installed - I’ll do some digging on it, I know there re tons of threads and google on it.

Update on my self diagnosis:

The next morning, my voltage gauge was moving much more than normal, just to double check the charging system, I had it tested at Autozone. Voltage regulator-failed. 20 min in the parking lot and $160 later, new alternator installed. ——re test — voltage regulator still failed [emoji849]

Then, front AC blower motor stops working, HVAC and AC all were working otherwise.... driving to the junk yard it comes back to life [emoji848].

Other things pointing to BCM:
-Radio hiss/high pitch after vehicle is sleeping
-Radio occasionally changes from XM when ignition turned off to am/fm on start
-Once asleep gauge cluster needles drop from zero then click back to life 30 seconds later and repeats continually (I sat in the truck for a long time...)
-month ago folding mirrors stopped working, then came back to life
-onstar light changes from green to red intermittently (replaced gps antenna and chased that squirrel already) it got better with new batteries

My first attempt to replace BCM, went to junk yard - I installed wrong (didn’t know) BCM- thought airbag light and rears windows would work after $80 no refunds...

Went to dealer to have it programmed $120 quote (gave me a discount out of pity afterwards to $87)

The good news, the radio/dash/charging gauge all were acting normal with junkyard BCM. Giving a strong confirmation of a failing BCM (but not 100% of course). The bad news, wrong BCM. Rear windows didn’t work/airbag lights still on.

At the dealer now, $330 for BCM and $225 for install and programming. The same tech discounted me the labor by about $75 bucks, which I’m glad...because it literally takes 10 min to swap the bcm with the only tools required a 10mm to disconnect the battery.

I’ll update once it’s done. And I bought a meter and will be doing a draw test after the bcm is completed.

Oh! Side note, on the way home that day, a stone smacked my windshield....16” crack ... $80 for repair [emoji51].

I wonder if there is a specific way to test the BCM?... unfortunately I think it’s a nightmare that requires close observation and a little bit of trail and error... my heart goes out to any mechs out there that have had to diagnose this before.

The way I look at it, I’ve got a brand new alternator that will probably last the life of the truck, and that $80+80 for bcm and programming was basically the “diagnosis” fee Vs handing it to a tech and trusting they are honest/correct.


Sent from my iPad using Tapatalk

 

[swathdiver]

Your symptoms are the telltale signs of a weak or failing battery and or corroded cables, poor connections. A Tech2 in concert with the shop manual is how to best diagnose every problem with these trucks.

 

[Meccanoble]

Dam, the money/time wasted through troubleshooting is frustrating. Cant really say anything to help with diagnosis but just wanted to say I feel your pain. Almost makes you want to throw the entire truck away .

 

[Awfiretto]

@swathdiver - yes - but also a failing BCM - the batteries are brand new and now so is the alternator. When the old battery was in the symptoms were more prevalent but they were still there with the new batteries. This was not the issue this time.


The tech2 would be nice, but considering the cost, along with the hassle of trying to find the files to download for BCM programming, I still most likely would have ended up at the dealer for programming. The way I look at this I got a new alternator and some experience that most likely still would have happened if I had a tech2. $20 scan tool from Walmart works great for pulling codes for now.


The service manager initially didn’t want to replace the BCM because after a flash he said everything was working as it should. I asked how he could test the BCM and he stated there’s no real way to do it, and I would have to leave it for observation to attempt to recreate the issues. A good honest knowledgeable tech , Jose from Munday Chevrolet in Houston TX. I appreciated the gesture but had him replace the BCM based on my diagnosis over the past months and long drives ahead. I bought this truck 3 months ago, and BCM started showing up in my search of symptom causes 2 months ago... I’ve watched it closely for months.


The new BCM is in and everything seems to be working well now. While I didn’t do a parasitic test prior to replacement of the BCM, I did one tonight. I’m at .03A (30ma). After all my digging this seems to be spot on, even with my 3 hot hard wired USB charging ports that replaced my cigarette lighters (green leds on them) https://www.amazon.com/dp/B07CVMDJRP?ref=yo_pop_ma_swf


The Onstar light turned red again on the way home from the dealer, so after the draw test I left the batteries disconnected long enough for a reset of the computers while typing this.


Some mosquitoes got in the truck during this time... a perfect excuse for a windows down “test” drive. A top speed governed run (first time for me in this) with a brake test and sprited driving, and multiple ignition cycles... the light stayed green the whole time!! Hopefully it will stay this way . @Meccanoble - this was enough for me to fall back in love with her... like make up **x .


As I log more miles I will become more confident in it all, and update one more time down the road.


In the meantime I am slightly more than semi confident this was the cause behind all my issues with the truck. And after some math, I figure a 30ma draw on two 70AH batteries should get me at the very minimum 30 days without a start before needing a jump!?! (Correct me if I’m wrong here). (Yes yes I know... providing I don’t have things plugged into the chargers)


Not sure if I’ll mess with an isolator yet or not, if I do it will be a simple relay type, that can be “jumped” in the event of a dead main battery... we will see... other option is a li-on jump pack in the back ‍. I’ve spent enough $$ for now and feel confident enough that system is solid enough as is to start reliably in most all conditions... and if not I’m almost always close to a jump.... and if not .. I have roadside.


TahoeYukonForums has definitely helped me get where I am today with this truck, and I hope this thread helps others. I may try to change the name on it to “solved - bad BCM diagnosis” after a few more days of driving.


Thank you all, and as I move forward I will do my best to document and post all my projects on the truck to hopefully helps others as well.

 

[arctictwist]

wow i literally traded in my last truck because of this. i didnt want the headache of tracking down the issue further than changing out the alternator and battery. It was a 2008 silverado and im about to get a 2012 suburban.... basically the same. so this is good to know!