2008 Yukon Hybrid

[DHC1]

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]

Moved to correct subform for you.

Welcome to TYF.

 

[tiktok4321]

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.

 

[DHC1]

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]

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]

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]

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.

 

[mtown27]

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

 

[dnt1010]

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]

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.

 

[Andrew l]

I received P0AC4 and P0AB9....any thoughts?

 

[tiktok4321]

Hybrid Battery. 90% sure. Had same problem, replaced, problem gone.

Sent from my Pixel 2 XL using Tapatalk

 

[BG1988]

I received P0AC4 and P0AB9....any thoughts?

got that code before


12V+ battery was bad... have it load tested (what is the age)

 

[Bradley P]

I know this is an old thread but I am having the same issues. When I ask for the Hybrid Transmission Control Module people act like I am asking for an alien part. Is this the same as the TCU?

 

[BG1988]

I know this is an old thread but I am having the same issues. When I ask for the Hybrid Transmission Control Module people act like I am asking for an alien part. Is this the same as the TCU?

P0AB9 is Autostop failed to restart engine


the Aux transmission pump & controller might need to be replaced since it's not HOLDING pressure correctly, it has two filters maybe the filter is clogged ?


or you can run it in M4 this will disable autostop and AFM for free but at best you will only get 20-21mpg city /21MPG highway this is the best i'm able to do) .




remember if you DO change the filters,ONLY change the filters and reuse the old fluid (if the fluid has never been changed you might have an issue with fresh fluid)



also get a sun shade for your windshield



i would check and see if the aux transmission pump wires are melted or have corrosion it's the bundle of wires with the white read blue yellow ( were the lower fuse box is) some people had this connector "melt" or have corrosion on the connectors

 

[BG1988]

I was checking with a volt meter wow the dip is huge when the engine resumes auto stop resume The voltage goes from 14.6 to 13.4

for a fraction of a second this dip could cause "computers" to shut down unexpectedly. from the power surge when it goes back to 14.6... and cause a stall out



I can see why this happens (i.e stalling or lagging )


120amps 1.6kw for the transmission pump is a huge load ( lets just say it's close to the rating of the two fueses for example)

 

[mtown27]

I've never changed the aux trans pump on the transmission but I suspect that it has caused some of my transmission problems. The only parts I've replaced to date are the aux module and two connectors. I think I may replace the aux pump itself but have not looked for a write-up on it yet. My truck has 220K miles on it now, and I think I replaced the pump around 150k maybe.

 

[Flexlo318]

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

Hey do you have a part number for this

 

[BG1988]

Hey do you have a part number for this

i got the part number for it 24261817 is the newer part #
What year are you converting from ? No chop kit

No sales tax estimated cost 292.48 including shipping and core

24261817 - Automatic Transmission Auxiliary Fluid Pump Control Module - 2008-2013 GM | World Parts Direct

Automatic Transmission Auxiliary Fluid Pump Control Module - 24261817. Genuine GM® Parts & Accessories. Manufacturer Warranty. From the Dealership to your Door.

www.worldpartsdirect.com

here is some more information on page 1 on the bottom of the page

https://static.nhtsa.gov/odi/tsbs/2014/MC-10112079-9999.pdf

Note: If ordering a control module for a 2008 or 2009 MY vehicle, also order connector p/ns 24259589 and 24259590.

Note: If ordering a pump for a 2008 or 2009 MY vehicle with the original control module, also order connector part number 24259588.

Note: If ordering a pump and control module for 2008 or 2009 MY vehicle, also order connector part number 24259590.

No chop the connectors!

 

[mtown27]

I ordered the aux trans pump this morning. Should have it within the next few weeks. I'll try and get some decent pictures and notes on the replacement.