GM Volt Forum banner
1 - 20 of 32 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
Our 2nd owner 2013 Volt entered limp mode while my son was driving home recently, soon after the vehicle had consumed the battery and switched to gas mode. He made the mistake of turning the car off at an intersection to see if "rebooting it" would put him back into normal drive mode. Instead, the car refused to start, right there in the intersection. With help, he managed to push it to a nearby AutoZone where they were able to pull the codes in the attached image. We then had the vehicle towed to a local Chevy dealer that said they had a certified EV technician. They told me that they would diagnose the problem for a flat $120. The contacted me later to say that they couldn't determine the problem without dropping the battery for another $1,600. I told them to hold off doing anything more until I could research this further. From all the research I've done over the last two days, I've not come across anyone who said that their battery had to be removed to be diagnosed, so I thing they are either ignorant or trying to fleece me. There were quoting me $12K just for the battery, if I recall correctly, if that were to be the problem.

I should point out that the car also bricked on the side the road about 4 years ago when it was still barely under warranty. At that time 1/3 of the battery was replaced with no cost to us, thankfully.

Can anyone here please advise me from reviewing the ODB2 codes on our Volt? Have any of you seen these codes on your Volt? What should I ask from the dealer from their initial diagnosis that would be helpful to include on this thread to figure out what is truly going on? I have read several people here saying that supposed HV battery problems are not actually so, and I don't want to fall into that trap. I'd love to find that we only need to replace the 12 volt battery or something simple like that. I've been reading up on the DIY battery swaps, just in case we have to go that route.

Thanks so much for your help.

David
172077
 

·
Registered
Joined
·
1,662 Posts
Seems like P1E23 is the key. The P1E00 simply means a module requested the check engine light be turned on. These are some very unusual codes. Has the 12 volt AGM battery ever been changed? When that battery starts failing, a lot of strange codes can result.

P1E23 This Diagnostic tests the checksum on RAM memory.

Auxiliary Transmission Fluid Pump Control Module Random Access Memory (RAM)

DTC Fail case 1:
Indicates that
HCP is unable to
correctly write
and read data to
and from Dual
Store RAM

DTC Fail case 2:
Indicates that
HCP is unable to
correctly write
and read data to
and from Write
Protect RAM
 

·
Registered
Joined
·
54 Posts
DTC P0AC4
Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0AC4: Hybrid Powertrain Control Module Requested MIL Illumination
Circuit/System Description
This DTC indicates the hybrid powertrain control module has set an emission related hybrid powertrain DTC. The hybrid powertrain control module sends a message via the
serial data circuit to the engine control module (ECM) requesting illumination of the malfunction indicator lamp (MIL). When the ECM receives the message, DTC P0AC4 will
set. The DTC information for the ECM will only display DTC P0AC4, but the freeze frame/failure records data may display the hybrid powertrain DTC that set.
Conditions for Running the DTC
• Vehicle ON for greater than 3 s.
• DTC P0AC4 runs continuously when the above condition is met.
Conditions for Setting the DTC
The hybrid powertrain control module has set an emission related DTC.
Action Taken When the DTC Sets
DTC P0AC4 is a Type A DTC.
Conditions for Clearing the DTC

you will need a GDS2 or Launch X431Pro to access into HPMC2 module and erase HV DTC error
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #4 · (Edited)
Thank you Junebug and Minorukun for your replies. I don't recall if the 12-volt battery has been replaced. Would you recommend replacing that as a trail-and-error first pass to see if these codes return? Is it enough to just check for a threshold voltage level on the 12-volt battery to see if is still good, or should I just replace it to eliminate any possibility of that being an issue? The cost is certainly trivial compared to the alternative things that could be done.

Can you confirm that the dealer is easily able to clear the existing codes that are keeping the vehicle from starting/operating to see if the same codes recur? It sounds like I would be wise to invest in a solution that will allow us to reset the codes ourselves, going forward, and to have more transparency into what is happening.

Is there anything more that I should ask of the dealer, as far as reports or testing to help narrow things down further vs just replacing the 12 volt battery and see what happens? Would you agree that it should not be necessary to remove the HV battery to properly diagnose?

Thanks.

davidaj
 

·
Registered
Joined
·
4,346 Posts
Thanks so much for your help.

David
View attachment 172077
The P1E23 is probably the key one. There was someone else that showed up with the same problem (about six months ago or so), we went the same go around, and last I know, he never came back with a resolution. I remember thinking at the time that it was PROBABLY going to come out that the Hybrid Control Processor aka Hybrid Control Module 1 which runs the power inverter that makes 3-phase AC out of the high voltage DC from the battery was going to be determined to be bad and need replacing.
 

·
Registered
Joined
·
1,662 Posts
Thank you Junebug and Minorukun for your replies. I don't recall if the 12-volt battery has been replaced. Would you recommend replacing that as a trail-and-error first pass to see if these codes return? Is it enough to just check for a threshold voltage level on the 12-volt battery to see if is still good, or should I just replace it to eliminate any possibility of that being an issue? The cost is certainly trivial compared to the alternative things that could be done.

Can you confirm that the dealer is easily able to clear the existing codes that are keeping the vehicle from starting/operating to see if the same codes recur? It sounds like I would be wise to invest in a solution that will allow us to reset the codes ourselves, going forward, and to have more transparency into what is happening.

Is there anything more that I should ask of the dealer, as far as reports or testing to help narrow things down further vs just replacing the 12 volt battery and see what happens? Would you agree that it should not be necessary to remove the HV battery to properly diagnose?

Thanks.

davidaj
I would replace the 12v battery with a proper Group 47 AGM battery. They are only $149 at Sams’s Club and just a few dollars more at PepBoys or NAPA. Easy to replace with a ratchet with metric sockets and an extension.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #7 ·
it was PROBABLY going to come out that the Hybrid Control Processor aka Hybrid Control Module 1 which runs the power inverter that makes 3-phase AC out of the high voltage DC from the battery was going to be determined to be bad and need replacing.
So, I've ordered a replacement 12-volt battery online to at least eliminate the cheapest solution, just in case. If that doesn't resolve the problem, what would be the next logical step to see if the Hybrid Control Module 1 is the culprit? How do I narrow the problem down further?
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #10 ·
I've got money on it being the 12v battery.
Me too - $167.99 for a Group 47 ACDelco replacement from Summit Racing Equipment. That's the best price I could find online, as the local Sams Club doesn't carry this battery group. I'm encouraged by your optimism about this being the problem. I am a little confused, however, in that a 12-volt battery's status shouldn't be a mystery. They are easy to check for voltage and capacity. I'm surprised people on this thread are not saying, "Check the 12-volt battery" instead of "Replace the 12-volt battery". I went ahead and bought a new one so that this variable could be completely eliminated. I'll report back when it arrives and is installed.
 

·
Registered
Joined
·
2,888 Posts
Me too - $167.99 for a Group 47 ACDelco replacement from Summit Racing Equipment. That's the best price I could find online, as the local Sams Club doesn't carry this battery group. I'm encouraged by your optimism about this being the problem. I am a little confused, however, in that a 12-volt battery's status shouldn't be a mystery. They are easy to check for voltage and capacity. I'm surprised people on this thread are not saying, "Check the 12-volt battery" instead of "Replace the 12-volt battery". I went ahead and bought a new one so that this variable could be completely eliminated. I'll report back when it arrives and is installed.
Checking the 12V battery is not as reliable as it gets it's charge from the HV battery. If you check it after turning off the car it may read 12+V but there is a slight drain on the battery and if a cell is suspect, when you go to start the car the next morning it may be too low to fire up the computers. That's why you should check it next day (or several days) after it has been sitting rather than check it after you've just come home which is what many people do not realizing, it can make a difference.
 
  • Like
Reactions: hellsop

·
Registered
Joined
·
4,346 Posts
So, I've ordered a replacement 12-volt battery online to at least eliminate the cheapest solution, just in case. If that doesn't resolve the problem, what would be the next logical step to see if the Hybrid Control Module 1 is the culprit? How do I narrow the problem down further?
Honestly, if it's a duff HCP, it's probably a job for an actual Voltec technician. This kind of repair is where you start playing around with the 400v circuits and other adventures. But based on your last experience where the dealer service decided that spending $1600 to drop the battery for exploratory reasons was the right path forward, I'm not sure that one is the best choice. I don't really have a good answer.

Replacing the 12v does sometimes clear bizzaro codes, but those bizzaro codes are ones that don't tend to persist past a simple off-then-on and they typically happen only at initial startup. That this happened after driving for long enough to run down the big battery, then set up after power-cycling when the 12v (as old as it is) is at its maximum capacity makes me feel that this isn't the issue.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #13 ·
if it's a duff HCP, it's probably a job for an actual Voltec technician
I just searched for the Hybrid Control Module and it appears they are readily available on eBay. I think that this is the unit that you are referring to. At $289 for the part, I would be fine if that turns out to be the problem as even the shop labor shouldn't be too bad in replacing that. That part appears to be the actual inverter as it has two pair of positive and negative terminals. Presumably one side is DC coming in and the other side is AC coming out. Is that the unit that you are referring to hellsop?
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #14 ·
So, I finally had a chance to take the new 12-volt battery down to the dealer and replace it in the back parking lot where out Volt had been relegated. Swapping out the battery was no big deal. As I was finishing up, one of the guys from the service department came out and asked how it was going. This was the first time I'd had any face to face conversation with anyone at the dealership. I explained the reason for replacing the 12-volt battery and admitted that I would be surprised if the problem could be that easy to solve but it made sense to eliminate that, just in case, based on the forum research I'd done. He then went on to explain that they don't rely on forums and that they "use "SI" from GM to determine what steps to take, and this is what is recommended". He went on to explain that two technicians had independently determined that the one of the three battery blocks had bad cells in it and the only way to narrow it down further (apparently from "SI") was to remove the battery and "bench test it". I then explained that that was contrary to my understanding but that I dare not argue the point with him, as I've never done this before.

So, help me get this right, forum - what level of battery condition is available from diagnostic testing through an interface with the Volt? How granular does it get? Would there ever be a reason to drop the HV battery for diagnostic testing?

Thanks for the education.

BTW, I told him that I wanted them to reset the system so that it would function again, so that we could drive it and see what happens. Not sure what else to do beyond that, but that is where we are. . .

Davidaj
 

·
Registered
Joined
·
4,346 Posts
Even with just a good OBD reader, you can extract the live voltages from each of... (I can't remember right now, about 90) cell groups that contain three cells. The difference in voltage between these groups is the "balance" of the pack as a whole, and there's a phase of charging at the end that's supposed to try to bring the lowest of those up to meet the rest. That's the "pack balancing phase" you might see posts about. Usually that works. But sometimes/eventually (or as a result of a programming bug that turned off the balancing phase -- there was a service bulletin about that) then the cell group might become damaged in a way that would prevent the balancing from working and that group would be permanently weak. Eventually that weakness becomes something that could actually cause the pack damage by overcharging the other groups, and then there used to be a program that would replace one of the modular sections of the battery for about $3500 in parts and a couple of days of shop labor. That "module section" seems to have gone away and now batteries as only as whole multimodule sections (and cost $10k instead of $3500). So yeah, pack health can be determined to a pretty granular point, but can't be fixed that granularly.

But I'm still not clear how that leads to the HPCM1 motor controller end of things codes being thrown rather than HPCM2 battery end of things codes if it's a battery issue. I guess that's why I'm not a Volt tech, just a guy with a manual.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #16 ·
Thanks for the detailed answer hillsop. You confirmed what I understood about being able to read voltages at the cell or cell group level. When quoting prices, they first threw out something about $12K for the entire battery. When I balked at replacing the entire battery, they came back and quoted me three different prices for each of the three sections that added up, more or less to the $12K. Apparently they can still get them in thirds but I suspect are being steered away from that by GM. Remember that they replaced 1/3 of my battery under warranty several years ago.

Like you said, things don't seem to add up with the codes we got using an ODB2 reader vs what they are saying is wrong. Actually, they are not really telling us what is wrong beyond, "You need to replace the battery". Maybe that is what they do when they have no other ideas? I don't know.

Interestingly, as I was composing this just now, I got a text from my contact at the dealer saying, "My tech just brought me the paperwork. He said that he has tried but the codes will not reset. So there is nothing we can do till that big battery is reset. I will get your paperwork turned in to the cashier." Are you kidding me! I responded, "What do you mean when you say, "till that big battery is reset"? Her response 10 minutes later was, ". . . I am sorry I mean till the high voltage battery is replaced or whatever cell is bad in it is replaced. Till that is done, my tech said it won't allow us to reset any of the lights, he tried but won't start at all and won't allow us to reset the lights. So it will have to be towed out of here."

They've clearly washed their hands of dealing with my vehicle if I'm not willing to replace the battery as they say is needed. So frustrating! I guess I'll go to the dealer tomorrow and insist on copies of the error codes that they got and whatever information they can supply me that has led them to this conclusion. I'm not willing to accept that the car is effectively totaled and not drivable without replacing some part of the battery. Maybe that is the problem, but they need to prove it to me based on data retrieved from the vehicle and not just tell me that the battery had to be dropped to be "bench tested". It really seems like double talk to say that the battery needs to be replaced but that it needs to be removed to be tested further.

Any thoughts on any of this (anyone)? Could it be possible that the Volt might refuse to reset the codes so that it can be driven again?

172134


Davidaj
 

·
Registered
Joined
·
1 Posts
Thanks for the detailed answer hillsop. You confirmed what I understood about being able to read voltages at the cell or cell group level. When quoting prices, they first threw out something about $12K for the entire battery. When I balked at replacing the entire battery, they came back and quoted me three different prices for each of the three sections that added up, more or less to the $12K. Apparently they can still get them in thirds but I suspect are being steered away from that by GM. Remember that they replaced 1/3 of my battery under warranty several years ago.

Like you said, things don't seem to add up with the codes we got using an ODB2 reader vs what they are saying is wrong. Actually, they are not really telling us what is wrong beyond, "You need to replace the battery". Maybe that is what they do when they have no other ideas? I don't know.

Interestingly, as I was composing this just now, I got a text from my contact at the dealer saying, "My tech just brought me the paperwork. He said that he has tried but the codes will not reset. So there is nothing we can do till that big battery is reset. I will get your paperwork turned in to the cashier." Are you kidding me! I responded, "What do you mean when you say, "till that big battery is reset"? Her response 10 minutes later was, ". . . I am sorry I mean till the high voltage battery is replaced or whatever cell is bad in it is replaced. Till that is done, my tech said it won't allow us to reset any of the lights, he tried but won't start at all and won't allow us to reset the lights. So it will have to be towed out of here."

They've clearly washed their hands of dealing with my vehicle if I'm not willing to replace the battery as they say is needed. So frustrating! I guess I'll go to the dealer tomorrow and insist on copies of the error codes that they got and whatever information they can supply me that has led them to this conclusion. I'm not willing to accept that the car is effectively totaled and not drivable without replacing some part of the battery. Maybe that is the problem, but they need to prove it to me based on data retrieved from the vehicle and not just tell me that the battery had to be dropped to be "bench tested". It really seems like double talk to say that the battery needs to be replaced but that it needs to be removed to be tested further.

Any thoughts on any of this (anyone)? Could it be possible that the Volt might refuse to reset the codes so that it can be driven again?

View attachment 172134

Davidaj
I am not a volt expert however as an owner I have a keen interest in the technical aspects of this car.
I have attached a page from the Volt workshop manual for these DTC codes.
It simply says
If the DTC is set, program the T6 drive motor generator power inverter module. If the DTC resets, replace the T6 drive motor generator power inverter module.
Perhaps the dealer can try to do this for you. Power inverter module can be an expensive item therefore you need to be sure before proceeding to change this module which is located within the engine compartment to the right of the engine.
It looks like the HV battery contactors remain open when this fault is set and there is no power available to run the motor until the DTC fault is addressed.

As for the battery condition I normally check the individual cell voltages using a smartphone app called MGV ( My green Volt). If you plug in a ELM327 bluetooth dongle ( Around $10 from eBay)to the diagnostic port it can display the cell voltages of all 96 individual cells. If there is a big variation in the voltages then the battery could be at fault. The ingition switch has to be on for taking these readings.

Hope this helps.
 

Attachments

·
Registered
2017 Volt Premier 80k+ Miles
Joined
·
694 Posts
If there is another Volt certified dealer unaffiliated with the current dealership, then it may make sense to take it there and see if they reach the same conclusion.

On a side note having two battery failures in less than 10 years (if actually the case) is pretty bad.
 

·
Registered
Joined
·
3 Posts
Very interested in what outcome you have. We are dealing with a nearly identical situation with a 2012. Trying to figure out what the options are. Car died earlier this week. Dealer wants $10k to replace whole pack, 8400 for battery, 1600 to install. Not putting that kind of money into the car but it seems silly to scrap it.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #20 ·
Not putting that kind of money into the car but it seems silly to scrap it.
I'm right there with you on that. I'll certainly let the forum know what I can come up with. Do you have reasonable confidence, based on codes from the system or a test of the battery cell voltages using the MGV app mentioned by [email protected] above, that the battery truly needs to be replaced?
 
1 - 20 of 32 Posts
Top