08 HYHO stalling randomly (without codes) - details inside
 

My 08 HYHO recently started stalling, several times pulling away from stoplights, a few times slowly climbing my steep driveway, a once backing out of my driveway. Below are a few details. I'm trying to keep this thing running for another 18 - 24 months (kid's college tuition) so I'm hoping someone can suggest where to look next.

1. About 4-5 years ago, I was having the braking issue others have had, high revs when applying brakes and sluggish starts from a stop (almost like a clutch was slipping.
2. Dealer replaced the Aux Trans Pump computer and all was fine for about 3 years.
3. Two years ago I started getting stalling a few times a month when taking off from a stop. All of the normal HV battery codes being thrown, but I was able to limp the truck another year.
4 Last summer (2020), the HYHO was stalling several times a week and became a major safety issue when you are making left-hand turns and you never knew when it would stall in the middle of the intersection. I took my HYHO to the "biggest" GMC/Chevy dealership in the SouthEast - thinking they would be able to diagnose properly. Even though the HV battery was deemed shot (thanks to those here on the forum and especially S Keith), the dealer thought it was everything BUT the HV battery. They wouldn't sell me HV battery until they went through all of their "checklist" BS. Basically wanting to replace everything BUT the HV battery. So, I let them replace the AUX Trans Pump last summer. Within a week, the same stalling was back! Back to the shop and this time they said it was the inverter causing the issue. Um, hell no I'm not replacing everything because of your "checklist".
So...
5. Bought a GreenBean battery last July (2020). NEVER had another issue until 2 weeks ago.
6. A month ago, while getting my tires rotated, the firestone shop tested my battery (which was about 18 months old) and deemed it as being bad. I'd been having zero issues. So, they replaced the battery (Interstate 730 or 740 CCA).
7. A few weeks after that, my engine rev'd up a bit and wouldn't go into Auto Stop until I turned the truck off, and back on. This grabbed my attention as I've unfortunately have seen this before I replaced the HV battery, but I haven't had it happen again, since it did it 2 weeks ago. A couple of days after that, I started to get the stalling - this time they are happening several times a day - No codes are being displayed, but one time I had a pending Aux Trans Pump code (it's now gone and hasn't appeared again when I pull codes with Torque). The stalling is not dependent on day or night driving (warm days with AC cranked up and cool nights with the AC on low with the windows down. I assumed the Greenbean was going bad, but S Keith looked at my log and seems to think the HV battery is fine.
8. So, troubleshooting...what changed? The 12v battery being replaced. Is it possible that the new 12v battery is bad as well? So, had Autozone hook up their tester and the battery tested at 100%.
9. Of course when I am logging with Torque, it never stalls. :D
10. Now I'm scratching my head. Could low trans fluid be the cause (I'll check the level tomorrow)? Could the new Aux Trans Pump be bad, even though it was replaced by the dealer last summer? Could the Aux Trans module be crapping out again? Hmmm, maybe the cheap OBDII Bluetooth device being plugged in all the time could be causing it?

Any next troubleshooting thoughts are appreciated and thanks in advance!!

Re: 08 HYHO stalling randomly (without codes) - details inside
 

There are a number of codes Torque can't read. This is a common thing on the Toyota hybrids too. What are you using to read codes?

Re: 08 HYHO stalling randomly (without codes) - details inside
 

Just Torque and a cheap OBDII bluetooth device. Is there something else you recommend? I'm trying to avoid my local GM dealer until I have to - they pissed me off so much, I think I have PTSD! :D

Re: 08 HYHO stalling randomly (without codes) - details inside
 

I know my Snap-On Ethos Pro will read anything the car can throw, but that's pretty spendy. It might be worth taking to an independent garage with a professional diagnostic system.

Re: 08 HYHO stalling randomly (without codes) - details inside
 

you did have both filters replaced could be plugged filter(s) I Would also check the grounds too.. and wires(maybe even replace them and upgrade them)


the electrical system is only as good as the WEAKEST link in the system and the AUX pump can draw 100 amps a resume

it's a Power sagging issue you can watch the voltage sag under load when it restarts




this suggest the Capacitors are failing in the 12VDC inverter it self or bad wire(s) somewhere.. or a faulty current sensor(see if any ground wires have bypassed the sensor such as after market equipment)



also make sure the battery cables are fully sit to the battery (ALL the way down the battery post as possible )(sometimes they can come loose )






YES i have the exact same issue you have with the A/C running




a sudden voltage sag could cause computers to go offline and "stall out the engine"



I know a lot about computers THEY don't like voltage sagging or being given too much voltage.... I thought about installing a smoothing Capacitor.... my self


I have seen about upto 2 volt drop(from 14.6 to 12.3vdc) while it auto restarts this means it's drawing 200-300 amps like a normal engine starting or BAD wire
This causes the typical Auto stop lag



Just turning on the headlights will drop it from 14.6 to 14.0 to 14.2.. this possibly indicates a Wire issue somewhere

I think if it i goes below 11.8 or so the computer shuts off = stall out



I manually Restart the engine manually by shifting into M4 and have the A/C off when i get to a light.....(to prevent engine revving )




The battery cable part numbers are 22759056 for the negative cable $56 on ebay (includes a new current sensor) and 22758936 for the positive cable 40$ on ebay...



also see this:

Microsoft Word - Document1 (autocodes.com)

Re: 08 HYHO stalling randomly (without codes) - details inside
 

Update - dealer diagnosed (based on P1AE3 and P1A88) to be the Battery Electronic Control Module located in the 300v battery. However, they can't locate the part, in the US, and no ETA to getting one!

Re: 08 HYHO stalling randomly (without codes) - details inside
 

it's 3500$ for a new one ouch
1000$ core charge 2010-2013 GM Drive Motor Inverter 12645548 | GM Wholesale Direct

12594086, 12636012, 12645548, 24243417, 24243426 12636016

$900 for a re-manufactured
confirm with the seller before buying Make sure it's the correct part :)
GM OEM-Power Module 24251562 | eBay

Re: 08 HYHO stalling randomly (without codes) - details inside
 

Thankfully that pricey item isn't what's wrong with mine.

Re: 08 HYHO stalling randomly (without codes) - details inside
 

Keep an eye out on eBay or check your local salvage yards for a battery. Swap the whole battery or swap the module and get it for less.

Re: 08 HYHO stalling randomly (without codes) - details inside
 

High Voltage Interlock System Circuit (P1AE3) seems to be what's killing my truck. Weird that the ONLY time it stalls is when it's sitting still, either auto-stop or with the engine running (happens in both D and M4). I'm really curious as to why the Tahoe doesn't die while moving. Almost makes me think a transmission sensor is screwed up...or, a computer is crapping out. Something is out of whack that it only stalls when sitting still