08 Yukon 160k miles, once vehicle is hot after about 30 min driving, come to a stop and it won’t go. Check engine light comes on and after a few min it will move but very slowly. Took it to a dealership they said it was the 12v had that replaced... same day same problem... replaced the aux trans fluid control module.... same day same problem... replaced hybrid battery (Greenbean reconditioned)... next day same problem... please help I can’t keep throwing money at things that don’t fix the problem! Codes are:
p0ac4
p0bbd
U0074
p0c11
p0c13
p0c14
p0c16
c0895

 

i don't think it's the transmission pump that runs at 12Volt AC 3 phase

those tend to have an auto start lag and is fixed by making sure the 12volt battery is tight and clean connections at the battery terminals(or replacement with a new 12v+ battery first ) before replacement of the Aux transmission pump...


99% of the time it "fixes it" as it has done to mine


I would raise hell to that dealer if they scammed me into claiming it was the battery.. and then spending thousands and turns out to be something else..
i'm sure you all ready spend about 3,500-4000 all ready for nothing...


basically replacement of random parts and hope it fixes it?


if it is the Aux cooling pump, the pump is about 50$ I highly recommend you have a professional install it though since it will be in the HIGH VOLTAGE area under the hood

p0ac4 is a Generic code (Just for the check engine lamp)




Inverter temperature codes
check the hoses that cool the power inverter might be broken or Aux water pump is bad

as the electronics is on another cooling loop from the engine (since the engine is 100C or 212F and don't want your inverter at 100C)
according to this

https://www.electronicdesign.com/aut...al-mode-hybrid

• p0c11 OVER TEMPERATURE protection!
• p0c13 OVER TEMPERATURE protection!
• p0c14 OVER TEMPERATURE protection!
• p0c16 OVER TEMPERATURE protection!

P0BBD is Voltage Deviation is high (secondary: causes 12volt system battery current min battery temp )








it's just telling us what is happening i.e the power is not what as expected as your inverter is overheating and not coughing up the 13.7-14.4 volts it's expecting to see.




since you replace the battery we know it's not that but the inverter codes help a lot

U0074 Bus Shorted condition has occurred to

C0895

The Electro-Hydraulic Power Steering (EHPS) operates when voltage at the EHPS connector is in the range of 34-50 volts.

DO NOT KEEP driving it you will burn out the inverter You may have gotten screwed by the dealership and bought stuff you did not need

the hose to the inverter might be damaged causing it to over heat

OR the AUX electrical water pump has failed(but not throwing a code)

or
you have a short somewhere which is drawing HIGH amperage

But not likely since it happens exactly at the same 30min

 

thank you for the quick response, Yukon is at my shop right now (I’m a painter not a mechanic lol... obviously!) and I will be at the shop tomorrow and take a look at the hoses. Is there a way to check the coolant level in that system to see if it’s been leaking or is it a contained and concealed system?

 

i think it uses a push/pull (or two pumps) setup i'm not 100% sure I 'm just guessing based on the setup

if it has a second pump i guess it would be located in the passenger headlight area





there appears to be one connected to the radiator area going directly to the inverter...(like i said i'm not interested in taking it apart to find out)




Yes just check the coolant reservoir it's interconnected with the main water pump it should have a line minimum and max lines on it


ONLY open the cap WHEN COLD if it's low
you don't want hot coolant on your face if it needs some coolant... dexcool 50/50 mix only or make your own 50/50 mix using concentrate (makes 2 gallons of 50/50 mix for the price of 1 gallon)

 

I think I got the “too hot” problem worked out. The was a fan relay in the fuse box that was loose and also was a little low on coolant. Drove perfect for a week. Last night I was idling for a about 20 min after about 20 min worth of driving and while I was idling auto stop never engaged. I went to leave backed out fine but when I went into drive it seemed to have no “power”. ICE RPMs would climb to 3000 but vehicle would barely pull. Pulled over shut it off. Nothing was over temp or odd. Started back up check engine light came on and drove home (abt 6min) fine. Drove it to work this morning (20min), and it drove fine. Ran the codes and this is what I got...

 

What is causing the P0AC4? Did you read the Hybrid controller?

 

Just read all codes vehicle wide... I’m assuming it was the “manufacturer specific DTC” don’t know what the actual code is bc scan tool said NA. But it had all the freeze frame data.

 

P0AC4 will be from engine computer. It is the code telling you that the hybrid computer wants the Check Engine Light on.

The Freeze Frame has information about what the truck was doing but it is in pieces and sideways.

The hybrid will have a stored code and the Freeze Frame for it as well. The engine should have the code causing the P0AC4

 

Yes that is what I was thinking, but there were no other codes other than the p0ac4 and “NA manufactures specific DTC”. And that was a vehicle wide code search for drivetrain, hybrid system, body, a/c, and everything else.

 

Expand the other module "boxes" in the app you are using (orange bars with exclamation marks) to possibly see additional codes. If that still won't show other codes, then that tells you that app you are using is junk and I would recommend the "Torque" app. I think it is $5 but does give all codes. The manufacturer of the OBD2 device you are using may also have a free app.