2008 Yukon Hybrid

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DHC1

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Hybrid tends to stall/shut off coming out of Auto Stop mode on occasion. Looking for feedback as to the possible root cause? Auto code pulled is P0AC4 which refers to the PCM/ECU. If I remove the Hybrid disconnect and 12v battery will I have issues with power components when batteries are reconnected?
 

soulsea

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Moved to correct subform for you.

Welcome to TYF.
 

tiktok4321

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I'm going through this exact issue right now. First thing to check is that all electrical connections are tight. This includes the 12v terminals and all hybrid connectors under the hood and that one that connects to the tramsmission control unit.

That's a starting point. Ensure that the Internal combustion engine is working flawlessly. Then have a DEALER ensure that the HCU and the TCU have the latest firmware and connectors are good.

Other than that, I have not had a definitive solution to my problem yet. In fact, the dealer keeps telling me nothing is wrong, $115 at a time.
 
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DHC1

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Did you have any codes to go off? I got P0AC4 code which indicates that it is a possible PCM issue! Just dropped it off at the dealer for a diagnosis. If i get anywhere with them i will update you!
 

tiktok4321

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My codes always cleared after a few hours. Unfortunately, I have had some major problems with my ICE and AFM. I don't think I'll really be able to diagnose the other crap until the mechanical engine is working well.

But, yes, I would like to know what your dealer says.
 

tiktok4321

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Hybrid tends to stall/shut off coming out of Auto Stop mode on occasion. Looking for feedback as to the possible root cause? Auto code pulled is P0AC4 which refers to the PCM/ECU. If I remove the Hybrid disconnect and 12v battery will I have issues with power components when batteries are reconnected?
So, after all was said and done with fixing everything on the internal combustion engine and the connections, etc., I have determined that whenever you get the dreaded P0AC4 code, it almost always requires a new hybrid battery pack. What did your dealer say? Any updates?

If you are in the Eastern US, there is a fairly new company out there called GreenBeanHybrid. They'll put a remanufactured battery installed at your home for $2,349. It comes with a pro-rated 5-year warranty (after 36 months, it's relatively worthless). It may be an option. I've found allegedly new batteries for around $2800, plus shipping, plus core. Shouldn't be hard to replace yourself, but these Green Bean guys will do all that - remove the old, install the new, reset the codes, reprogram if necessary, in your own lot.
 

mtown27

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I went through this during the summer with the 2008 as well. After many hours of research and working with the dealer, I replaced the Hybrid Transmission Control Module in the front of the engine bay, located under the battery. It was about $500 for parts only and I did it myself. You’ll need the module plus two new harnesses. (Unfortunately it’s pigtail only and you have to build your connections yourself, and it is NOT a wire for wire swap!!!). I changed the harnesses and module in under 2 hours. The truck had to relearn the module for a few days, doesn’t go into auto stop during this time. It has worked and never stalled on me since. It’s not an easy job necessarily due to the dumb harnesses. The hybrid guy at the local GM dealer had never replaced one himself so I had to do everything myself. But I promise it’s the solution.

79CB37E9-FCBE-477D-AAC8-57A7CE0856BF.jpeg
 

mtown27

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I went through this during the summer with the 2008 as well. After many hours of research and working with the dealer, I replaced the Hybrid Transmission Control Module in the front of the engine bay, located under the battery. It was about $500 for parts only and I did it myself. You’ll need the module plus two new harnesses. (Unfortunately it’s pigtail only and you have to build your connections yourself, and it is NOT a wire for wire swap!!!). I changed the harnesses and module in under 2 hours. The truck had to relearn the module for a few days, doesn’t go into auto stop during this time. It has worked and never stalled on me since. It’s not an easy job necessarily due to the dumb harnesses. The hybrid guy at the local GM dealer had never replaced one himself so I had to do everything myself. But I promise it’s the solution.

View attachment 189210

Here’s the harness and pigtails

8055FD92-CD21-41BE-83CF-61E0D14F518F.jpeg
 

dnt1010

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Mtown27 it has been over a year since you posted and I was curious if your fix held up or if it actually turned out to be the Hybrid battery pack was bad? The POAC4 and POBBD code is supposed indicates a +1.5 differential in the hybrid battery internal module voltage. If the 7.2 volt modules get to 1.5 voltage differential they are probably pretty much used up. I had an issue a few weeks back where POAC4 and POBBD popped up. The Tahoe drove erratically with hesitation from stop going into ICE etc. just like the OP described. After a couple of drive cycles the code went away and it is driving normally now but at 10 years old and over 200k miles I suspect that it is in fact the hybird battery pack and I have ordered a new one. Supposed to be in tomorrow. I was afraid of the GreenBean battery as they are reusing old used battery modules most being 10+ years old that they supposedly recondition. I want my ole ** to drive like new. Nothing but the best for my ole ** Hahaha
 

mtown27

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Since I changed the control module and harnesses, it has not stalled once at any point. During my troubleshooting (I think 2016), it would stall multiple times per week. I made the change, the computer relearned itself, and has been clear since.
 

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