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Discussion Starter · #1 ·
Background:
Hi all, I have one of the very early Chevy Volts, I am the second owner, and the car has been virtually hastle-free its entire life. It now has 125,000 miles on it. It started having a problem last year when it sat in the driveway without being plugged in to the high voltage charge port or driven for approximately two months (in the summer). When I started driving it again, the car had a dead 12v battery. Given that the battery was a Delco and may have been the original unit that shipped with the car, I figured it didn't owe me anything and replaced it. I am a HIGHLY competent shade-tree mechanic (trans rebuilds, diff upgrades, engine retimings, engine rebuilds, etc.), so changing a battery is a cakewalk. But that's when the problems started.

The problem:
When the car has had its 12v battery disconnected and the large orange fuse in the center console pulled out for an extended period of time, like it was when I swapped the battery out, the car runs like it always did for about a day, even if you drive it over 100 miles (as I've done several times). When the battery power runs out in this state, the engine comes on quietly and smoothly at low RPM, and the car's power delivery feels completely normal. However, usually within a few restarts or the next morning, the car will no longer switch to electric power, Mountain Mode is unavailable, and the car runs incredibly hard (3500-4000RPM) during regenerative breaking and at anything above residental neighborhood speeds. The car's acceleration is noticably slower than normal, and the gas mileage is absolute trash (18-20MPG highway), and I'm worried I'm going to hurt the engine running it so hard and so continually. No matter how far I go with it in this state (again, 60+ miles sometimes), the car will never revert to electric power, or if it does, will do so for maybe 1 mile, then switch right back again to running hard. Although the car did throw the "service high voltage charging system code" a few times in this condition (I checked the coolant levels and the battery for leaks), it typically won't have any CELS even after weeks of driving it this way. The car accepts a charge as normal, but does not allow the use of the stored battery power during driving. On the rare occasion that CELS do occour, the codes tend to be:

P1E00
P1FFF

and sometimes
P0AA6

I stopped hunting down the source of the problem this spring when it seemed to go away with the warmer weather. During the summer it did not recur, but this winter it's back with a vengance. I have tried checking the battery coolant levels, and just got the SHVCS defeat plug yesterday but, although I've only driven it 5 miles so far, the behavior seems to be exactly the same as before--ran great when I first hooked everything back up yesterday, as always, then this morning Mountain Mode was unavailable again, and even with the car warmed up and outside temps around 45F/7C, it runs hard and doesn't seem to want to switch to gas. I am positive the plug was installed correctly, all codes were cleared before hand, etc.

We have lived in this location, with these winters, for a number of years, and it never behaved like this before last year. I'm completely at a loss as to what's going on. I checked the harnesses, but don't see any obvious wiring damage in the areas I can get to without pulling a lot of stuff out of the engine bay.

Anybody have any ideas?
 

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HVCS defeat plug? You mean the *** Sensor retrofit that replaces the battery coolant tank sensor? Once the error is set, installing that sensor defeat won't restore or turn off the error. It needs to be installed before the error occurs rather than after.
 

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16,17 volt
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had the same temp variant, high voltage isolation, isolation relay in battery box mine was done under warranty
 

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You said the problems started after replacing the 12v battery. Did you replace the original Delco with a proper AGM battery? A regular flooded lead acid battery will cause trouble.
 

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I'm came here since I have the same problem. It is constantly running on ICE while not using any electric. It's in the 50's temp and I drove it around 12 miles without EV ever kicking on but somehow 3kwh used while I didn't have any heat on. Occasionally I have the CEL blinking on heaving driving as well but no code sticks. If it does it's P0030.

171587
171588
 

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I'm came here since I have the same problem. It is constantly running on ICE while not using any electric. It's in the 50's temp and I drove it around 12 miles without EV ever kicking on but somehow 3kwh used while I didn't have any heat on. Occasionally I have the CEL blinking on heaving driving as well but no code sticks. If it does it's P0030.

View attachment 171588
You need to put some air in those tires. Factory guidelines say 38 psi, but most of us here run 40-42. Yours are at 33-34 and the right front is showing yellow.
 
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I'm came here since I have the same problem. It is constantly running on ICE while not using any electric. It's in the 50's temp and I drove it around 12 miles without EV ever kicking on but somehow 3kwh used while I didn't have any heat on. Occasionally I have the CEL blinking on heaving driving as well but no code sticks. If it does it's P0030.
Your symptoms seem consistent with running a Fuel Maintenance Mode (i.e., running on gas, even with some available battery power). As you drive in Extended Range Mode, it’s normal for the battery state of charge to cycle above and below the "switch to gas" state of charge, and if you turn off the car during an FMM when the cycle is slightly above that SOC, the next time you start the car (especially if you plug in overnight and the next start is on the next day), the motor will use that small "overcharge" of kWh before the gas use kicks on.

Has it been several months since you last put gas in the tank? It should be possible to confirm an FMM by looking at the center console touch screen display when you start the car - that’s where a message should appear briefly telling you an FMM is in progress. Further info on the FMM is available in the owner manual.
 

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...However, usually within a few restarts or the next morning, the car will no longer switch to electric power...

...then this morning Mountain Mode was unavailable again, and even with the car warmed up and outside temps around 45F/7C, it runs hard and doesn't seem to want to switch to gas...

Anybody have any ideas?
So, which is it... "does not allow the use of the stored battery power during driving,,," or "doesn’t seem to want to switch to gas..."?

You write, "within a few restarts or the next morning" after this 2011 Volt has been driven far enough to deplete the battery, "the car will no longer switch to electric power, Mountain Mode is unavailable, and the car runs incredibly hard (3500-4000RPM) during regenerative breaking and at anything above residential neighborhood speeds. The car's acceleration is noticeably slower than normal, and the gas mileage is absolute trash (18-20MPG highway), and I'm worried I'm going to hurt the engine running it so hard and so continually."

To me this sounds almost as if your 2011 Volt is attempting to extend the range by driving exclusively on generator output because, for some reason or another, it can’t "borrow" power as needed from the battery.

The Gen 1 Volt is propelled 100% of the time by the larger motor MGB, and when the battery is depleted, the motor, in effect, is "unplugged" from the battery and plugged into the generator output. Generator output is usually sufficient to meet demand in moderate driving conditions. When a demand request is made that can’t be met by generator output, that power is "borrowed" from the battery buffer and recharged when demand is reduced.

I don’t really know if this can happen, but consider this: if your Volt can’t "borrow" power from the battery (which might provide a clue why Mountain Mode won’t work - Mountain Mode temporarily increases the "switch to gas" state of charge to increase the amount of "borrowable" power, and the system is not letting you borrow any power), then the generator must work harder to meet the power demand (engine runs harder), especially at above-residential street speeds. When the generator is running hard to meet demand, other performance factors are reduced (acceleration slower than normal would be a sign of this). The generator’s fuel consumption rate would also soar to keep up with demand, dropping the "gas" mileage.

I would think that if too much demand is made and the generator can’t supply it at maximum output, the system would be forced to borrow enough power from the battery to drop the state of charge too close to the "hard floor" level, which should then trigger a Propulsion Power Reduced episode, further reducing the car’s performance until the battery SOC can be restored to the proper level.

Perhaps, though, when your system switches the fuel source for MGB to the generator output, an error disconnects it entirely from the battery (i.e., it can neither charge nor discharge the battery), so you won’t trigger a PPR through excessive demand, but you’ll just lose performance until power needs = output capability. This MGB/battery interaction could be evaluated... if you live in an area where there’s a long downhill drive, then if you "coast" down that long descent while driving in L with a less than fully charged battery (or on level terrain, take your foot off the accelerator while moving at a moderate speed or higher), the regenerative braking system should normally put some regen into the battery. This is more noticeable in L than in D. Any regen braking effect would indicate the system is allowing MGB, working as a generator, to recharge the battery (sort of the reverse of "borrowing"). Would an inability to use regenerative braking while descending a hill (particularly if the battery was not fully charged) be an indication that the battery/MGB configuration has problems?
 

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Discussion Starter · #10 ·
It's probably not fuel maintenance mode; the car literally gets worse gas mileage than my old Lingenfelter Z06 did, so it's probably been through 10+ tanks of gas since this problem started up again this fall.

It's also not a non-AGM battery.

I got VCX Nano and am going to use the Delco software to try and figure this out after Christmas.

Thanks for the good ideas, I'm learning a ton.
 

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Adding a few gallons of fresh premium fuel is far cheaper than pursuing other options. Taking it into a Chevy dealership with a qualified voltec service technician is probably the best bet. I can change oil, rotate tires, change brake pads, but the electronics and the high voltage system requires a service manual and potentially specialized tools.
 

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I'm having the same (or very similar) issue on our 2011, with 112K. Just posting to hopefully get an update from the OP. Did you ever get it resolved ShortTrip?
This forum is a great resource. Thanks to all who contribute!
 

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It's probably not fuel maintenance mode; the car literally gets worse gas mileage than my old Lingenfelter Z06 did, so it's probably been through 10+ tanks of gas since this problem started up again this fall.

It's also not a non-AGM battery.

I got VCX Nano and am going to use the Delco software to try and figure this out after Christmas.

Thanks for the good ideas, I'm learning a ton.
I’m sorry, but as a Vette owner, if your Volt is getting less MPG than a Z06, something is terribly wrong…

Here’s to getting things resolved and I hope it’s a simple fix!
 

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I'm having the same (or very similar) issue on our 2011, with 112K. Just posting to hopefully get an update from the OP. Did you ever get it resolved ShortTrip?
This forum is a great resource. Thanks to all who contribute!
You might want to create a new thread, it looks like the OP may not update us as to what went wrong.
 

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Discussion Starter · #15 ·
Bump. $1800 wasted at the dealer, and not a bit better. It only happens below 50 degrees, and never when it's above 60. Still trying.
 

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Sorry to hear that you are still having the problem ShortTrip. What did the dealer try for $1800?
Just an update on my similar issues:
My 2011 w/ 113K is still doing strange things. IIRC, the most consistent code, P0C78, indicates a problem with the high voltage contactors in the battery case or a current leak to ground (loss of HV battery isolation.) However, the car runs normally most of the time. Today I started driving with 20 miles on the GOM; put it in Mountain Mode and GOM dropped to 13, as expected. After driving about a mile, the chime sounded and DIC message "Mountain Mode Not Available" illuminated briefly and the GOM showed 18 miles electric and 56 miles gas available. MM was grayed out for the next couple miles of that trip. About an hour later, I drove home and MM was still grayed out. I was on battery power the whole time.
This behavior is different from what I was seeing when I posted a couple months ago (above.) At that time, my problem was like yours, i.e., running on gas when there was plenty of battery power available.
We continue to limp along. Meanwhile, I get more confused the more I learn and experience with this little Engineering Marvel.
Thanks to all who contribute!
 

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Sorry to hear that you are still having the problem ShortTrip. What did the dealer try for $1800?
Just an update on my similar issues:
My 2011 w/ 113K is still doing strange things. IIRC, the most consistent code, P0C78, indicates a problem with the high voltage contactors in the battery case or a current leak to ground (loss of HV battery isolation.) However, the car runs normally most of the time. Today I started driving with 20 miles on the GOM; put it in Mountain Mode and GOM dropped to 13, as expected. After driving about a mile, the chime sounded and DIC message "Mountain Mode Not Available" illuminated briefly and the GOM showed 18 miles electric and 56 miles gas available. MM was grayed out for the next couple miles of that trip. About an hour later, I drove home and MM was still grayed out. I was on battery power the whole time.
This behavior is different from what I was seeing when I posted a couple months ago (above.) At that time, my problem was like yours, i.e., running on gas when there was plenty of battery power available.
We continue to limp along. Meanwhile, I get more confused the more I learn and experience with this little Engineering Marvel.
Thanks to all who contribute!
Hey guys. I also own a 2011 Volt (2nd owner) I’ve driven it 30,000 miles for 2.5 years. And last winter it got a little crabby and wouldn’t engage gas mode. And the dealership had no answers and fortunately it didn’t act up again until this year. This winter was exceptionally cold in Socal. And it did that a few times and now it doesn’t engage battery mode only operating in gas mode. Getting that worse than ZO6 mpg 🤣. But it’s warming up today (58°) and I’m fully confident when the battery gets warm and happy it’ll go into battery mode again. Volts just hate the cold. Let’s not try to overthink these 10+ year old cars.
 

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As per the service manual:
The isolation check for P0AA6 Hybrid Battery Voltage System Isolation Lost runs when all the contactors (main positive, main negative contactor, multi-purpose contactor, charger positive contactor and charger negative contactor) are open. This check monitors isolation in the drive motor battery system. This check runs only once during the time that the hpcm2 is awake and runs after the contactors have been open for 10 seconds. This monitor typically runs when the vehicle is turned off after a drive. It could also run when the vehicle is first started, if there is a long enough period between the hpcm2 waking up and the main contactors closing.
High voltage isolation can be lost due to a shorted battery heater, not uncommon at the 10 year mark, especially if coolant not exchanged every five years and mixed with de-ionized water. (distilled water will lead to electrical isolation faults, de-ionized is less conductive). This pack heater lives on the BECM (battery energy control module) at the front of the main propulsion battery and requires pack removal to replace. It would only be energized when temps are low and the pack is cold.
 

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Hey guys. I also own a 2011 Volt (2nd owner) I’ve driven it 30,000 miles for 2.5 years. And last winter it got a little crabby and wouldn’t engage gas mode. And the dealership had no answers and fortunately it didn’t act up again until this year. This winter was exceptionally cold in Socal. And it did that a few times and now it doesn’t engage battery mode only operating in gas mode. Getting that worse than ZO6 mpg 🤣. But it’s warming up today (58°) and I’m fully confident when the battery gets warm and happy it’ll go into battery mode again. Volts just hate the cold. Let’s not try to overthink these 10+ year old cars.
I had to smile when I read this. I had just asked my son how the Volt behaved over the last couple of days. He recounted how it sometimes ran on battery and mostly ran on gas. He said, "One time it even said Engine Running Due to Temperature. It just doesn't like the cold."
He's not overthinking it.
Unfortunately, many of us have been trained as engineers and we tend (to a fault) to want to understand WHY machines do what they do. In spite of that, I'm becoming increasingly inclined to see the wisdom in your approach to these crabby cars that don't like the cold.
I'm going to try not to overthink it. Really... right after I check the codes again and try to make sense of the MGV screens.
Serenity now!
Happy New Year.
 

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i run my volt in -40 weather and have no trouble with my gen 2 other than the cabin heater
when engine running due to temperature, motor runs a lot off and on keeping the motor temp between 64c and 53c even when it has battery
sound to me like your heater for your traction battery is dead
other posts have said that it starts to work at 16c and colder
so if your hv/traction battery is cold the car does not want to make it available
your engine when it comes time to use the extra power from the battery is denied the engine has to run harder and give you bad fuel mileage and your battery doesnt drop
so - heater or module that controls it and i think thats the becm
thats my guess :)
 
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