P0C2B and P0AC4 DTC codes

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HybridBatterix

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Hi everyone,

sorry for my english, i'm french.
I have a 2007 Tahoe hybrid with some problems.

I have a good experience on HV Battery, usually, i do diagnostics on Toyota, Lexus, Honda.

In 2019, a dealer of american vehicles near Paris (France) called me for making safe the vehicle because they had to change the gear box.
They changed the gear box, but the problem is always there.
So, i did a diagnostic with Torque (i put the good pids).
And i saw the High Voltage battery is bad.

The dealer decided to stop calling me.

One month ago, the new owner of this Tahoe called me, and he wants to fix the problem.
I dismantled the High Voltage Battery. It's really bad, the ECU near the HV Battery is in short-circuit, there is oxidation, severals pins are blue.

We ordered a new ECU. I checked the harness with voltage taps. I learned to dismantle the pods on an used Toyota harness, in case i need to change the harness too.

I changed the ECU, the 40 modules, the copper plates. I cleaned the fan, i dried it.
I put it all back together.

I tried to start, the ICE doesn't sart.
I looked for the origin of the problem. I found this forum. We check two plugs below the fuse box.
The ICE starts few seconds and stops.
The two DTC code i have are P0C2B and P0AC4.

P0AC4 is juste the engine light on on the dashboard ?

P0AC2B is a bad Feedback Signal of the Auxilliary Transmission Fluid Pump Control Module ?

Someone can confirm ?

I saw there is a Service Bulletin. I found in another thread in this forum.

Thank you very much.
Max


PS : the dealer of american vehicles gave me the GM process to make safe the Tahoe.
On Toyota, to make safe, we have to disconnect the 12V battery before to disconnect the fuse on the orange plug of the HV battery.

But, on the GM vehicles, the process says to remove the orange plug of the HV Battery several minutes to disconnect the 12V.
It's true or it's a bad translation english to french on the process ?
 

BG1988

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i would check the wires they get corrosion just disconnect the 12v+ since the pump is the 12v only and controller is 12v.. maybe damage wire? i would also check the 60amp fuse as well

Auxilliary Transmission Fluid Pump Control Module is under the 12+vDC battery tray in the bay area. NOT in the high voltage battery housing ....

if they replaced the transmission look to see if they even bother to connect the AUX pump to the power supply this might have been something over looked or the connector did not match (NO need to chop wires as they have an adapter for it) we would have to see both connectors to get the right one

since the wire changed in MY2009/10

if it's connected i would check and see if all 3 phases are working since it's a 3 phase 14v motor..aux pump.. if one of the phases failed then the Auxilliary Transmission Fluid Pump Control Module cooler failed and/or aux pump....

there is also a chance they hacked/chopped the wires in ?


if the pump is working then i'd look into the fuel pump also making sure teh ignition system is working correctly

as the engine will in fact start on a bad 'HV battery'
 
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HybridBatterix

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Hello,

thank you very much for your answer.

I will check it this next days.
I'll come back to give you more infos asap.
 

BG1988

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HybridBatterix

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Hello,

first, we found the 60amp fuse was bad, it had melted, we changed it.
We try to start, the Tahoe doesn't start.
Then, i checked the wires. They look like good. I don't see anything, no scratch, no damage, no oxidation on the lugs.

The dealer changed the transmission with the pump, the transmission fluid pump looks like "new" as the gear box.

For the moment, I suppose the transmission fluid pump works.

I saw the adaptator between the AUX pump and the module output 4 wires.

I have 12V at the input (5 wires cable) of the module. But i don't have 12V at the output (4 wires cable).
When i try to start the Tahoe, at the output i can measure several volts but it decreases. After few minutes, i have 0 Volt.

I opened the AUX fluid pump module, i tested the continuity with multimeter.
The 5 wires cable (input) is good, no cut off.
The 4 wires cable (output) is good, no cut off.
I didn't see burn marks on the mainboard.

The messages on the dashboard are the same with the module and without the module.

I think the problem comes from the AUX transmission fluid pump module itself.
The reference is 24261817 i found it here :

Thank for you help.
We will buy the module and i'll install it. I hope the problem will be resolved with this part.
 
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HybridBatterix

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Hi,

i received the new AUX fluid pump module, the 5 wires cable had not the same connector so i had to change with the old one.
I cut and i used inline wago to connect the 5 wires cable to have the good connector.

I have the messages again : check battery charge system, repair hybrid system.
I have a new message : check antitheft system

I will check the 5 wires cable is good and read the DTC codes.
 
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HybridBatterix

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Hi,

I succeded to reset the antitheft system, the alarm rang.

And the Tahoe started ! But it shut down few minutes later.
I check the messages on dashboard : check battery charge system, repair hybrid system.

I don't have any DTC code with my diagnostic tools.

But the voltage of 12V battery decreases.

So it should be probably the dc dc converter.
The dc dc converter for 2008 Tahoe hybrid is : 24251562

I found it here :
GM Part direct

On GM Part corp, it's the same reference.

It's good ? Someone can confirm the reference of dc dc converter ?

Thank you very much.
Max
 

BG1988

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Hi,

I succeded to reset the antitheft system, the alarm rang.

And the Tahoe started ! But it shut down few minutes later.
I check the messages on dashboard : check battery charge system, repair hybrid system.

I don't have any DTC code with my diagnostic tools.

But the voltage of 12V battery decreases.

So it should be probably the dc dc converter.
The dc dc converter for 2008 Tahoe hybrid is : 24251562

I found it here :
GM Part direct

On GM Part corp, it's the same reference.

It's good ? Someone can confirm the reference of dc dc converter ?

Thank you very much.
Max
i would check to make sure the battery cables are connected correctly to the 12v battery (or faulty 12v battery) this can prevent charging or low system voltage (12v battery shims are a must on this SUV to prevent issues )
 
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HybridBatterix

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Hi,

thank you very much.

I think the 12V battery is good. It's not old, two years old.
We did several charge cycling before to put in the car.
I checked with voltmeter.
But to be sure, we can try with an other one.

For battery cables, on the studs positive and negative, it's ok. I checked.
Maybe, check again and contact cleaner.

It would be the first time i have problem with battery cables from the DC Converter ends on hybrid vehicle, but why not.
In France, we say : "there has to be a first time for everything".

We ordered the DC Converter, so i check this advices before to replace the DC Converter.

Check list :
1) Check the battery cables on the studs
2) Try with an other 12V battery.
3) Remove the Inverter (after security setting)
4) check the DC Converter and cables to link the 12V battery.

Max
 

BG1988

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these cables actually crush the posts really bad to the point (mine would not charge at all it would get to like 13.0-12.9 i though mine went bad) what is the voltage when it's turned on? same as the battery or slightly higher?


after i put the shims it was 14.8v-14.9v 13.6-14.5 now days because it's correctly charged
 

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