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Discussion Starter · #1 · (Edited)
2018 Chevrolet Volt (~65k miles)

Fault codes:

POAC4 - Powertrain
POC04 - Powertrain

From OnStar:
electric drive unit 13_25

Dropped off at dealer on 08/15/22. Took 15 days for them to tell me the 12v battery was bad and that no further diagnostics could be performed until I agreed to buy a new 12v battery. I tested this battery myself before dropping it off and told them as much. I reluctantly agreed to a new battery hoping they would find the real culprit. A couple days later they say it’s fixed, but all they did was replace the good 12v battery with a new one and reset the system. I was livid. $518 for nothing. They reassured me the issue was absolutely fixed now despite never fixing P0C04. It promptly died again on the highway the very next day.

Now they’re just contacting me today to inform me they think it’s related to the transmission and that it WILL NOT be covered if it’s mechanical in nature instead of electrical.

This sounds like total BS. I’ve contacted GM several times, but they all pretend to know nothing about the Voltec warranty and just give me the runaround. Every. Single. Time.

I thought the Voltec warranty covered the hybrid powertrain? Or is there any truth in the dealership’s statement that only transmission issues of an electrical nature are covered?



Edit to add summary of failure details: Check engine light appears. Propulsion power lost while in drive. Shift to park message displays while still in drive. After coasting to a stop selecting any gear will display the shift to park message. Car is unable to move in any gear. Occasionally after a short rest period the car can drive a brief distance before all the symptoms reappear.
 

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2011 Volt Premier (0737); 2010 Highlander Hybrid; 1993 K3500 6.5TD former ambulance
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Seems like your dealer is trying to use a very narrow (and incorrect) reading of the language in the upper right, on p.13 of the manual shown in your post: "...warrantable repairs to the specific electric propulsion components of the vehicle."
They are reading it as: "...warrantable repairs to the specific electric propulsion components of the vehicle."
I believe it is intended to be read as: "...warrantable repairs to the specific electric propulsion components of the vehicle."
As an example of non-electrical parts of the Voltec system being covered, many early Volts had the bad stator bearings replaced under warranty.
Good luck!
 

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$516 for a 12V battery says a lot. The battery is about $200 retail, and it takes about 15 minutes to replace by anyone with a 10mm socket wrench. So they charged $1,260/hour to replace that battery.
 
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Discussion Starter · #6 ·
Yeah, they hoisted the Jolly Rogers on me for sure. I feel like they just let the 12v battery die so they could claim it was the problem and keep their $150 diagnostic fee since the 12v battery isn’t a warranty item.

They promised they wouldn’t charge anymore than $227 + $40 labor for the battery and the ~$150 diagnostic fee. Somehow that still came out to ~$518 in an area where the tax rate is about 7 percent last I checked.
 

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2012 Std w Nav
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Fault codes:

POAC4 - Powertrain
This one's irrelevant. It's the HPCM1 version of the HPCM2's P1E00: "Please turn on the MIL/idiot light"
POC04 - Powertrain
That's the spunky one, in any regional dialect you care to apply.
From OnStar:
electric drive unit 13_25

Dropped off at dealer on 08/15/22. Took 15 days for them to tell me the 12v battery was bad and that no further diagnostics could be performed until I agreed to buy a new 12v battery. I tested this battery myself before dropping it off and told them as much. I reluctantly agreed to a new battery hoping they would find the real culprit. A couple days later they say it’s fixed, but all they did was replace the good 12v battery with a new one and reset the system.
important question time: What did they mean by that? What they're supposed to do for this is clear the codes, test the car, and see if the code pops again. If it doesn't, it's fine. If it does, something's up. But they should have been the ones to do that test, not giving it back to you claiming it was fixed.
I was livid. $518 for nothing. They reassured me the issue was absolutely fixed now despite never fixing P0C04. It promptly died again on the highway the very next day.
I'm assuming with the same P0C04 code. But you haven't said, so...
Now they’re just contacting me today to inform me they think it’s related to the transmission and that it WILL NOT be covered if it’s mechanical in nature instead of electrical.

This sounds like total BS. I’ve contacted GM several times, but they all pretend to know nothing about the Voltec warranty and just give me the runaround. Every. Single. Time.
It's not a transmission. That code is VERY SPECIFIC. It sets when one or more phases of MGB draw more than 600 amps. Which is Quite A Lot at nearly 400v. That kind of power can move trains. I think they keep calling it a "transmission" because it's kind of stuck on the engine like a transmission might be, but the power inverter/motor controller, the electric motors and the planetary gears are pure Voltec.
I thought the Voltec warranty covered the hybrid powertrain?
It does! Generally speaking, the "powertrain" warranty covers the engine up to MGA. There's some argument about whether the final drive (a reducing gear from the planetary set to the wheels) is "powertrain" or not, but it's completely simple and basically never fails, so it doesn't come up much.
Or is there any truth in the dealership’s statement that only transmission issues of an electrical nature are covered?
At this point, who knows? Because it's not a transmission issue. It's a MGB or powertrain electronics (aka motor controller) issue.
Edit to add summary of failure details: Check engine light appears. Propulsion power lost while in drive. Shift to park message displays while still in drive. After coasting to a stop selecting any gear will display the shift to park message. Car is unable to move in any gear. Occasionally after a short rest period the car can drive a brief distance before all the symptoms reappear.
Yeah, the car is unable to move because the first thing the car does when that code is set is to disable the HV battery. Because the worst-case as far as the car is concerned is that there might be a short someplace in the powertrain electrical supply currents going to the MGB motor. And we don't want things melting or bursting into flames if we can help it, so the big battery gets disabled.
At this point in the process, where the code comes back after testing is to push it back into the shop and start looking for shorts between those big fat orange wires. If there comes back current flow between any place where there shouldn't be current flow, they replace MGB. If there isn't, then they update the software on the HPCM1, and try the "drive around the parking lot a couple of times" test again to see if the code comes back. If it does, they replace the powertrain electronics box (yes, the whole thing), and if it doesn't, the software update counts as the fix. It's a lot of work to resolve the "replace the expensive bits" but it absolutely should be Voltec warranty and it's not at all complicated.
 

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Discussion Starter · #8 ·
Thank you for the detailed response. It is greatly appreciated.

Yes, they did state that they test drove the vehicle after replacing the 12v battery and “resetting the system”. I assume they just meant clearing the codes. They claimed they were unable to duplicate POC04 at the time.

The last time it died it showed POC04 again. I also had the dealer confirm the reading this time.

I get the feeling they want to charge me more money to look at it any further. Last I spoke with them they were going to contact a “techline” and see how they wanted to proceed. It didn’t make me feel all warm and fuzzy inside…
 

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Two items down from the item circled in the warranty booklet that you posted is for the Electric/Hybrid Drive Unit. That is the transmission. I think it is covered...
 

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2011 Volt Premier (0737); 2010 Highlander Hybrid; 1993 K3500 6.5TD former ambulance
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I think you need if possible to get it to a more reputable dealer with more volt experience


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Yeah, or you need to have a discussion with the dealership's management and come away from that discussion with confidence that they will "straighten out and fly right", as my dad used to say.
1) They either have a certified Volt Tech or they don't. I presume they do if they are engaging techline. I also presume that they'll begin to RTFM (Service Manual, in this case), which will lead them to do the things that @hellsop mentioned above.
2) Once you determine whether you have a competent technician who is following GM troubleshooting steps, you will still want to determine if the management is crooked or just ignorant of the Voltec warranty. I think you have a strong case for substantial reimbursement of what you've already paid (for the probably unnecessary and certainly overpriced 12V battery replacement.)

Just my two cents. Again, good luck!
 

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Thank you for the detailed response. It is greatly appreciated.

Yes, they did state that they test drove the vehicle after replacing the 12v battery and “resetting the system”. I assume they just meant clearing the codes. They claimed they were unable to duplicate POC04 at the time.

The last time it died it showed POC04 again. I also had the dealer confirm the reading this time.

I get the feeling they want to charge me more money to look at it any further. Last I spoke with them they were going to contact a “techline” and see how they wanted to proceed. It didn’t make me feel all warm and fuzzy inside…
It's a scary moment, not knowing what's going on, but .... part of that is that one almost never gets to talk to the techs who know what's in the manual (presumably) and instead get everything filtered through service reps who, while being very friendly people, frankly don't have time or interest in doing more than getting you to go away. Contacting techline is a good step. They're now treating this seriously. It'll GET fixed. Just keep correcting "transmission" to "hybrid drive system" to help them remember to bill it under the Voltech warranty, and scour the internet for a PDF copy of the service manual, and practice hitting control-F a lot, so you can ask good questions, and you'll come out of this okay.
 
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