2008 Tahoe Hybrid 12v Battery Constantly Dying

[Dirtrunner702]

Hello,

I have a 2008 Tahoe Hybrid. All software up to date. 5-6 year old 300v battery pack and 2 year old 12v battery. No CEL or issues at all and regularly maintained.

About 4 weeks ago it would not start in the morning. Nothing had changed or had been changed up to that point.

Took it to the dealer and they Replaced the negative battery cable and new 12V battery, they did an airbag recall on it as well. Went to get it the following day and the service manager said it started but all all sorts of lights came on, traction control, air bags, etc.
They kept it and decided to replace the SDM-C module under driver seat. Came back to get it and all was good. Took it home.

2 days later it wont start, same as before. Turn the key and the CEL light turns on and eventually things light up but no crank.
12v Battery drained. No Crank

Replaced OEM battery with Optima yellow top ( Dealer said the battery they put in tested fine, but wont start the truck) and it drove PERFECT for 2 days

Proceeded to do a parasitic draw test every way that you can do one and found a big draw coming from Fuse 25 DSM (Driver Seat Module and Remote Control Door Lock Receiver which also does the Tire pressure monitoring sensors). Pulled the fuse 25 and draw goes from 70-112mA draw down to 50mA. Ive done these tests where you do not interrupt the power to the vehicle so as to not lose its state while connecting a multimeter.

Replaced the battery AGAIN with a brand-new Optima because the previous optima would not let the truck crank, even after charging it overnight. Drove around without the RCDLR and with the new Optima batt, then it started to show symptoms of a low charged 12v battery after 3 days.

Im back to square 1.

I am waiting for a new positive battery cable assembly to arrive as I am completely out of ideas and the battery terminal does feel hotter than normal after driving for a few tests making sure the electrical system is charging the battery while its on. No CEL, no service hybrid system errors or anything.

Does anyone know what the mA draw should be when the tahoe is fully asleep? I know 50mA is a little high but maybe thats normal for this year range tahoe?

TLDR: Everything perfect and one morning no crank. Took to dealer and they replaced negative battery cable assembly and 12v battery. Issue returned and they replaced SDM-C module. Got a new Optima battery and it also died after 2 days. Narrowed parasitic draw to RCDLR. Pull and it drops mA fluctuation from 70-120mA down to 50mA while asleep. Purchased ANOTHER Optima batt and 3 days later the battery died again even with RCDLR disconnected.

Ive Been pulling my hair out on this for 3 weeks. Thank you for reading and any input is HIGHLY appreciated. I love this thing and want to stay in the no car payment club but fear something else major may be wrong, perhaps in the hybrid RAP system. I dont know.

 

[BG1988]

is it even charging? like 14.5-14.8v on cold start?

 

[j91z28d1]

yeah I wonder if it's charging while it's on? can you check the voltage at the battery while it's running?

battery drains are so ******* newer vehicles. it takes like 30mins for some modules to fully go to sleep in some vehicles. I've chased my tail for weeks over some newer Ford trucks.

I'd have to look up a spec, but 0.100amp doesn't sound like a crazy draw to kill a battery that quickly. especially a new yellow top.

I've had good luck with a DC amp clamp helping during t/s. you can get them pretty cheap off Amazon. don't really need to be fluke quality. just show you close enough. you can just clip over the battery cable after it's been sitting for a few hours to make sure everything is asleep and see what the drain is without disturbing anything

voltage drop test is the best way to check the cables. volt meter with on lead on the neg post of the battery, other lead on the block. it should be basically 0. if you have any voltage that shows its dropping voltage from a bad connection. do the same on the pos post to where ever the pos cable goes in these trucks. it's bit of a mess to follow haha.


only other guess and it's a complete guess is the brake module, it's mounted under the truck about the drivers seat area. few cases of guys having to replace them because water got up inside them. but I have no idea if that has power while the truck is off and it would probably throw a module code.

 

[ivin74]

Check the alternator fuse, it might be bad and the alternator might not be charging the battery.

 

[j91z28d1]

Check the alternator fuse, it might be bad and the alternator might not be charging the battery.

yeah these trucks are odd balls. they don't even have an alternator.

the electrical side is kinda crazy.

 

[BG1988]

yeah these trucks are odd balls. they don't even have an alternator.

the electrical side is kinda crazy.

yeah the 200 amp fuse can still be bad

you can leave an 1amp load overnight and it would still be fine (i.e leaving interior lights on)

 

[BG1988]

yeah I wonder if it's charging while it's on? can you check the voltage at the battery while it's running?

battery drains are so ******* newer vehicles. it takes like 30mins for some modules to fully go to sleep in some vehicles. I've chased my tail for weeks over some newer Ford trucks.

I'd have to look up a spec, but 0.100amp doesn't sound like a crazy draw to kill a battery that quickly. especially a new yellow top.

I've had good luck with a DC amp clamp helping during t/s. you can get them pretty cheap off Amazon. don't really need to be fluke quality. just show you close enough. you can just clip over the battery cable after it's been sitting for a few hours to make sure everything is asleep and see what the drain is without disturbing anything

voltage drop test is the best way to check the cables. volt meter with on lead on the neg post of the battery, other lead on the block. it should be basically 0. if you have any voltage that shows its dropping voltage from a bad connection. do the same on the pos post to where ever the pos cable goes in these trucks. it's bit of a mess to follow haha.

one cable goes to the fusebox and the other two goes to the AUX fusebox (next to the radiator )
One for the MEGAFUSE and other for the AUXfuse block...
inspection for corrosion might be necessary

 

[j91z28d1]

a tsb pops up. 08-06-03-008A

if you can find it it give a few things to check.

besides the normal make sure it's charging the battery while on, says onstar should be 3-20mA but can stay on standby for 48h and pull 250mA if it trying to get a call.

check the front and back hvac motors are shutting off at key off and some cars have afterblow enabled. it runs the blowers to dry the ac evaporators about 30mins after driving by running them for a while.


check for under hood relays struck on when key off, examples given cooling fan relay

a rear door lock relay sticking concern. that one says if you find that one sticking you gotta replace IP fuse box. the relay is internal and can't be replaced separately.

and circuit 1240 (left door) 1340 (right door) they run thru they left and right B pillar and might short, if so there's a 25amp fuse that should be hot to the touch. but it doesn't give a fuse number haha.

this bulletin is horribly written. not very specific but if you Google the number you can probably find and read it. other than that I see it can set a dtc
B1527
if the state of charge is 30% lower than last time the engine was running or the 12v battery drain is greater than 2 amps.

the bcm doesn't seem to care until it kills the battery by 30% from the last time your drove it, or the drain is over 2 amps. I'll attach the current drain chart. I'm not 100% sure this is hybrid specific but I did put the vehicle type and year in. but I do find this software sometimes brings up form general info if it doesn't have anything else to display haha.

 

[Dirtrunner702]

Thank you everyone! I will be doing all this today and tomorrow. I’ll see if I can find something to report back. I truly appreciate the input and time

 

[Dirtrunner702]

Hey all, Saturday night update. Replaced the 200amp fuse and made no change.

Confirmed the system is charging the 12v battery. At fresh crank it’s 14.7 volts and just fluctuates over 5-10 mins down to 13 and back up to 14 and such. Getting good voltage while ice runs and when in auto stop.

Craaazy thing happened. I was just wiggling everything that I can to see if I get anything strange and then bam! I wiggled the heater core hoses a bit and the AC compressor shuts off… almost like a short. The hvac controls locked up and the air bag light flashed a few times. I can reproduce by wiggling the hoses again.

So I have turned the truck off and put my multimeter in series without interrupting power to the system and will monitor for a while. I will take off the air intake and air box tomorrow and check all wiring down there. I hope I’m onto something here

 

[j91z28d1]

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.

 

[Dirtrunner702]

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

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!

 

[Dirtrunner702]

Pics for reference

https://imgur.com/FZSNqtm

https://imgur.com/eCvyWq1

https://imgur.com/SzPbKxh

https://imgur.com/alyKCzC

https://imgur.com/alp9Ir6

 

[j91z28d1]

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]

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

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.

 

[Dirtrunner702]

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.

 

[ivin74]

Do you have pictures of the old cable that shows the damage wire?

 

[Catvilledoorman]

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]

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]

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