2008 Tahoe Hybrid 12v Battery Constantly Dying

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j91z28d1

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heater hoses huh. definitely sounds like you have something either making a bad connection or shorting out. hopefully you find it.

be careful with any of the orange high voltage wires. if you do need to check them, the procedure is on a net somewhere but basically there's a disconnect plug in the back at the battery. pull that, and the 12v neg cable, wait about 5min and then you gotta test for voltage at the hybrid battery connector, like wire to wire and wires to ground(case) if you have 0. you're OK. if you have anything wait longer for the caps to discharge. I only say that because I wonder if you pull the cover off the inverter if you'll find one of the high voltage loose or something there or down at the ac compressor.
 
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Dirtrunner702

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Thank you for the advice! I was able to work around the HV cables and didn't die haha.

Gentlemen, I may have named this post incorrectly. The problem may have been a combination of issues.

The dealership replaced the negative cable but did not replace the Positive. I found this weekend that my positive cable terminal was not making a good enough connection to the 12v battery. I found the terminal cracked from underneath where the + cables are bolted onto the battery terminal connector, I could see shiny coper at what seemed like a seam, wiggling it or bending it gave the no crank/good crank symptoms. When I would remove it to charge the battery and plug it back in, I'm guessing it was hit or miss and sent me down the wrong rabbit hole.

Apparently when I did the test recommended here to see if the battery was charging, I had it connected in a way that it had a good connection and was giving me what I wanted to see but not what happens if the terminal is moved a certain way. This would explain the system not being able to charge the 12v batt correctly previously and making the terminal way hot to the touch. HINDSIGHT :Angry:

I still need to check if the truck continues to use between 60-120 mA spikes while its asleep, but all calculations say that high of a draw would take between 8-14 days to kill a battery just sitting. I could live with that. We use it almost every day.

Secondly, I found a short in the wire loom that goes to the HV controller under the hood. I think I saw a TSB on this about checking the loom for cutting from the metal band that holds the loom which is bolted to the passenger side head ( right around the heater hoses!! ) . I found 2 cables that were slighly cut into. The plastic cable management was burned from one side and not visible from a basic inspection with the intake tube off. Two of the cables were slighly cut into from the metal band that holds the loom and the other appeared to have over time had the sheath cut from one of the retaining clips holding the electric motor that feeds the in/out heater hose lines to the water pump. Electrical taped the cables and checked for other cuts and that was it. Retaped the whole loom and put the cable management back on. Kept the metal band but folded it in a way that will not cut again and used some zip ties to better hold the weight of the entire loom. Started the Tahoe and wiggled to test and the issue is no longer occurring where HVAC controls lock up and airbag light illuminates for a few seconds.

While I wait for the OEM positive cable assembly i used a spare battery terminal that I had and bolted the positive cables to it. Left it plugged in overnight and started just fine this morning. Will continue to check 12v battery voltage over the next few days of usage and will provide another update as I get more info on this nightmare.

Appreciate all the help!
 
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j91z28d1

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thanks for the follow up. sounds like you found it. looking at your pics I will check my harness there just incase.

these battery terminals are odd, never seen a quick release style on any gm car before and feels like I've seen 100s lol. has always left me wondering if they were thinking we'd need to disconnect the battery often. I can see them wearing out.

good catch.
 

ivin74

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Thank you for the advice! I was able to work around the HV cables and didn't die haha.

Gentlemen, I may have named this post incorrectly. The problem may have been a combination of issues.

The dealership replaced the negative cable but did not replace the Positive. I found this weekend that my positive cable terminal was not making a good enough connection to the 12v battery. I found the terminal cracked from underneath where the + cables are bolted onto the battery terminal connector, I could see shiny coper at what seemed like a seam, wiggling it or bending it gave the no crank/good crank symptoms. When I would remove it to charge the battery and plug it back in, I'm guessing it was hit or miss and sent me down the wrong rabbit hole.

Apparently when I did the test recommended here to see if the battery was charging, I had it connected in a way that it had a good connection and was giving me what I wanted to see but not what happens if the terminal is moved a certain way. This would explain the system not being able to charge the 12v batt correctly previously and making the terminal way hot to the touch. HINDSIGHT :Angry:

I still need to check if the truck continues to use between 60-120 mA spikes while its asleep, but all calculations say that high of a draw would take between 8-14 days to kill a battery just sitting. I could live with that. We use it almost every day.

Secondly, I found a short in the wire loom that goes to the HV controller under the hood. I think I saw a TSB on this about checking the loom for cutting from the metal band that holds the loom which is bolted to the passenger side head ( right around the heater hoses!! ) . I found 2 cables that were slighly cut into. The plastic cable management was burned from one side and not visible from a basic inspection with the intake tube off. Two of the cables were slighly cut into from the metal band that holds the loom and the other appeared to have over time had the sheath cut from one of the retaining clips holding the electric motor that feeds the in/out heater hose lines to the water pump. Electrical taped the cables and checked for other cuts and that was it. Retaped the whole loom and put the cable management back on. Kept the metal band but folded it in a way that will not cut again and used some zip ties to better hold the weight of the entire loom. Started the Tahoe and wiggled to test and the issue is no longer occurring where HVAC controls lock up and airbag light illuminates for a few seconds.

While I wait for the OEM positive cable assembly i used a spare battery terminal that I had and bolted the positive cables to it. Left it plugged in overnight and started just fine this morning. Will continue to check 12v battery voltage over the next few days of usage and will provide another update as I get more info on this nightmare.

Appreciate all the help!


Glad you were able to find the problem and report back.
 
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Dirtrunner702

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Howdy,

Happy to report that the + cable stopgap did prove one of the problems was at the original battery terminal/cables . The cables that were shorting out in the loom and repaired have made the issue with electrical issues go away completely. The new + cable assembly arrived and I installed it this evening. Voltage on the battery before replacing the cable is holding at a little over 13v with the truck off, after several days use, 14.7 with it running and has not had any more issues with no crank. Still seeing about 70mA draw spiking up to 120mA at full rest/asleep but perhaps that’s what thing uses by default. I really appreciate all the input and advice from you guys. I have to remind myself to never overlook the BASICS when beginning troubleshooting on this thing in the future. 6BC96516-D910-4F5D-96C6-3DB0C87CE373.jpegC34897AD-2D17-4660-A515-457ADFA0E317.jpegB8585D0E-C7CC-45C2-A4FC-60552FCF97DA.jpeg
 
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Catvilledoorman

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Dirtrunner702,
I admire your tenacity on this problem, just bought a 2009 with very similar issues, after key on, Autostop for a 1/2 hr or so, I get Service Charging System and Power Steering messages, PS stops working. Charge up battery, and wait a bit truck starts and all is good.

I appreciate your hard work, pics, and your follow-up reports very much. I'll be following in your footsteps. Thank you.

May start a new thread if I find new info.
 

tiktok4321

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Did these come from the factory with quick release? Mine had them when I bought it 2nd hand. They were eventually replaced for similar reasons.

These are good trucks. Just need a little TLC. Coming up on 290K now with: 1 new engine, 1 replacement Hybrid battery, 1 replacement AC Compressor, and a myriad of little things.
 

BG1988

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Did these come from the factory with quick release? Mine had them when I bought it 2nd hand. They were eventually replaced for similar reasons.

These are good trucks. Just need a little TLC. Coming up on 290K now with: 1 new engine, 1 replacement Hybrid battery, 1 replacement AC Compressor, and a myriad of little things.
yes it comes with quick release at the factory that is the oem cable
 

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