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2012 out of warranty (111k miles). High Voltage Charging System error with the P1E00, P1FFF, and P0A66 codes. Serviced three times. Sensor replaced the second time. The code returns within a day except after the sensor was replaced. Then it took about a week for the HVCS error to return.

In any case, I have been driving exclusively on gas for about 4000 miles including highway miles with no problem. Except for this HVCS issue, I love the car.

I have given up trying to have the charging system error resolved.

Is there any downside to continuing to run exclusively on gas?
 

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If you mean "will the car be damaged buy driving thousands of miles on gas without ever charging?" then the answer is no - the car will be fine.

That's what happened with a lot of the cars GE bought for their employees - they got a gas card with it, but GE didn't pay for electricity, with predictable results.

I feel like you lose a lot of the value of the car without electric driving so to my mind there are substantial downsides in terms of user experience and environmental friendliness, but the car shouldn't have any issues.
 

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That's too bad. On the bright side, it is a good thing that you have the option to run like that. Any other car with a major drivetrain problem would be a paper weight. I don't see any problem to running like that. If the source of your error is a failing battery, it is possible the battery will eventually get worse and have a negative affect on driving, such as putting the car into propulsion power reduced mode, etc. But as long as it is running well, I think it is fine to just keep driving it like that. I would do the same thing.
 

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2012 out of warranty (111k miles). High Voltage Charging System error with the P1E00, P1FFF, and P0A66 codes. Serviced three times. Sensor replaced the second time. The code returns within a day except after the sensor was replaced. Then it took about a week for the HVCS error to return.

In any case, I have been driving exclusively on gas for about 4000 miles including highway miles with no problem. Except for this HVCS issue, I love the car.

I have given up trying to have the charging system error resolved.

Is there any downside to continuing to run exclusively on gas?
You sure you don’t have a California VIN? They have 150k mike warranty.
 

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You’re not actually "driving on gas." The Gen 1's "gas mileage" is the distance you travel during which one gallon of gas is being used by the engine to run the generator.

I’ve been driving my 2012 Volt for 6+ years. My understanding is that when a Gen 1 Volt "seamlessly transitions to gas," what really happens, in effect, is that the large traction motor is "unplugged" from the battery and "plugged" into the generator’s output, and then runs on gas-generated electricity ("electric" miles = "grid electricity" miles, "gas" miles = "gas-generated electricity" miles). Under certain lower demand operating conditions (think of conditions experienced when cruising smoothly at > 35+ mph), the generator motor is clutched to the drivetrain to increase overall efficiency (better generator fuel consumption rate efficiency = better gas mileage). In this split-power configuration, ICE torque contributes directly to the propulsion torque.

A High Voltage Charging Error message suggests there’s a problem getting the high voltage battery to charge properly. Is it a faulty battery or a charging system problem? You could try using Mountain Mode’s "recharging" feature. By switching to MM while driving or when parked (the self-charging chevy Volt video shows a 2012 Volt being MM recharged while parked), a fully depleted battery should be recharged to the ~4 bar level in ~15 minutes using ~0.36 gallons of gas.

Switching to MM in a 2011/2012 Volt before the ev range has dropped to 0 will allow you to switch back to Normal and regain use of that MM-recharged power immediately. Using MM after the battery is fully depleted may require you to turn the car off and back on again to gain use of that MM-recharged power. When you use MM-recharged power in your 2012 Volt, it will count as Electric Miles without changing the kWh Used number (it’s not grid power).

If MM can successfully recharge your battery, then your error message would seem to indicate a problem with the recharging-from-the-wall system, perhaps a problem with the plug on the side of the car or the recharging circuits under the hood.
 

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2012 out of warranty (111k miles). High Voltage Charging System error with the P1E00, P1FFF, and P0A66 codes. Serviced three times. Sensor replaced the second time. The code returns within a day except after the sensor was replaced. Then it took about a week for the HVCS error to return.
Are you sure about those code #s? My 2012 service manual doesn't have the second or third listed. The first one is the generic HPCM2 asking for MIL that goes with anything powertrain related. It's an older electronic copy, but I wouldn't have expected there to be new codes on the same older cars...
 

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Are you sure about those code #s? My 2012 service manual doesn't have the second or third listed. The first one is the generic HPCM2 asking for MIL that goes with anything powertrain related. It's an older electronic copy, but I wouldn't have expected there to be new codes on the same older cars...
If you search the forums for P1FFF you get tons of hits. Only two hits when searching for P0A66. So they've been reported before.
 

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If you search the forums for P1FFF you get tons of hits. Only two hits when searching for P0A66. So they've been reported before.
Combined with Steverino's post above and the SHVCS message, that would make sense if he's having failed coolant sensor issues, since that's a retrofit for 2012s that might not have codes in the original manual.
 

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If the sensor was leaking you could have coolant wicked into the harness. I've seen harness wicking on extreme levels. It's startling to unplug a PCM for testing only to have power steering oil pour out. Some Dodges would get water in the ABS connector and what we learned is if one end of a connector is exposed to anything liquid, you'd better check the other end to see if it made it to the next connector. Most times, it did.
 

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If the sensor was leaking you could have coolant wicked into the harness. I've seen harness wicking on extreme levels. It's startling to unplug a PCM for testing only to have power steering oil pour out. Some Dodges would get water in the ABS connector and what we learned is if one end of a connector is exposed to anything liquid, you'd better check the other end to see if it made it to the next connector. Most times, it did.

If the battery coolant tank had a hole in it allowing coolant to travel horizontally along the bottom, hit the sensor, travel down the sensor, then travel up the wire, past the weather sealant gasket and into the sensor? Possible I suppose, and easy enough to check: has the the coolant tank run dry? If not, no leak.

It's more likely that sensor is doing what that sensor does: flake out, set an error, require a trip to the dealer where the dealer finds nothing wrong. They replace the sensor (they are like $6), clear the codes, send you home. At some point, rinse and repeat.

That's why some of us proactively replaced the sensor with one that will never throw a code, it's permanently neutered. The long thread I linked to goes into detail.
 

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Combined with Steverino's post above and the SHVCS message, that would make sense if he's having failed coolant sensor issues, since that's a retrofit for 2012s that might not have codes in the original manual.
It's in there. OP wrote P0A66 instead of P0AA6, that's all. Loss of High Voltage isolation. Which is... a non-trivial code. the last diagnostic step is "8. If all the circuit tests normal, replace the A4 hybrid/EV battery pack."
 

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Does it still function as a hybrid when running on ICE, or is the battery not doing anything? Carrying around a big heavy deadweight is a drag.
 

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Does it still function as a hybrid when running on ICE, or is the battery not doing anything? Carrying around a big heavy deadweight is a drag.
Since he's not reporting a Propulsion Power Reduced message and is loving driving the car, the car is allowing battery use in extended range "hybrid" mode. There's no way he would be so positive about it if the battery were locked down completely.
 

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If the battery coolant tank had a hole in it allowing coolant to travel horizontally along the bottom, hit the sensor, travel down the sensor, then travel up the wire, past the weather sealant gasket and into the sensor? Possible I suppose, and easy enough to check: has the the coolant tank run dry? If not, no leak.

It's more likely that sensor is doing what that sensor does: flake out, set an error, require a trip to the dealer where the dealer finds nothing wrong. They replace the sensor (they are like $6), clear the codes, send you home. At some point, rinse and repeat.

That's why some of us proactively replaced the sensor with one that will never throw a code, it's permanently neutered. The long thread I linked to goes into detail.
The condition usually occurs when the sensor leaks internally at the pins. The weather seals only protect from the outside, and do a good job of keeping the liquids and elements out. They also do a good job of keeping liquids in the cavity in as well, and it'll run straight up both wires to the next point of termination.

I found a bulletin for this that also calls out checking and replacing the jumper harness for the coolant sensor.

https://static.nhtsa.gov/odi/tsbs/2013/SB-10052204-5938.pdf
 

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The condition usually occurs when the sensor leaks internally at the pins. The weather seals only protect from the outside, and do a good job of keeping the liquids and elements out. They also do a good job of keeping liquids in the cavity in as well, and it'll run straight up both wires to the next point of termination.

I found a bulletin for this that also calls out checking and replacing the jumper harness for the coolant sensor.

https://static.nhtsa.gov/odi/tsbs/2013/SB-10052204-5938.pdf
Wait, you are saying the sensor has liquid inside that is leaking out? If so, that is not addressed in the PDF you attached (thanks for that by the way). There is no instruction to inspect the sensor for internal leakage.

As far as I know, the sensor does not have an fluid inside that would leak out. Plus, it does not address why multiple replacements would fail. Are they all leaking? Again, no mention of leaking sensors as a condition or a cause in the diagnostic PDF.

Replacing the harness is called for if the diagnosis shows there is an internal wire break in the harness. That can happen, or the connection to the main harness could be faulty. But if those check out as OK, and there is no leak in the coolant tank or inside the battery, the end result will be the dealer replacing the sensor. When that sensor fails, they will rinse and repeat. When that sensor fails... you get the idea. Stop the insanity.

For many, the sensor is the issue. That's where the WOT Sensor replacement comes into the picture.
 

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Wait, you are saying the sensor has liquid inside that is leaking out? If so, that is not addressed in the PDF you attached (thanks for that by the way). There is no instruction to inspect the sensor for internal leakage.

As far as I know, the sensor does not have an fluid inside that would leak out. Plus, it does not address why multiple replacements would fail. Are they all leaking? Again, no mention of leaking sensors as a condition or a cause in the diagnostic PDF.

Replacing the harness is called for if the diagnosis shows there is an internal wire break in the harness. That can happen, or the connection to the main harness could be faulty. But if those check out as OK, and there is no leak in the coolant tank or inside the battery, the end result will be the dealer replacing the sensor. When that sensor fails, they will rinse and repeat. When that sensor fails... you get the idea. Stop the insanity.

For many, the sensor is the issue. That's where the WOT Sensor replacement comes into the picture.
There are a couple different kinds of sensors and I may be in error in assuming the sensor has contact with the coolant, thus making a leak possible. The other kind of sensor uses a float and either a hall sensor or a simple reed magnetic switch, and does not contact the coolant directly.

I'll have a closer look.
 

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There are a couple different kinds of sensors and I may be in error in assuming the sensor has contact with the coolant, thus making a leak possible. The other kind of sensor uses a float and either a hall sensor or a simple reed magnetic switch, and does not contact the coolant directly.

I'll have a closer look.
This sensor is not inside the tank, it's not submerged in coolant. It's outside the tank, a remote sensor. The hypothesis is the sensor fails due to a combination of temperature and vibration, not leaking coolant. The failure appears to be within the internal bussing that is encapsulated in a sealed "potting" epoxy of the reed switch.

But the fact is the original sensor will fail eventually and often the replacement sensor will as well. Bad design. So far, there are no reports of the car getting the error on cars equipped with the sensor defeat. I and others had had the defeat on our cars for years, no issues.
 

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You should get one or two ohm reading if the (reed switch ) is open or closed and I guess zero if you pull off the cable.

The picture posted in an older thread was not in English

WOT even told us in 2012 not to play with the cables to the sensor as that triggers these codes and a trip to dealer to re-flash would be needed. ( we now know that disconnecting the 12 volt battery before playing with the sensor should prevent that )

If the problem is voltage issolation in battery cooling fluid there should be other codes ?

This quick fix added in 2011-2012 need to be re-thought and re-programmed. ( or the WOT super duper plug )

After 7 years of 98 % electrical battery use I too am a ICE only car for the last month

---I do get a 4 bar charge in MM mode---
 

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Slightly different scenario - matches the thread title. I moved into a condo rental that lacks any access to at home charging (my state has a law that entitles units to establish separate metering for their assigned parking, but I'm a renter). My employer also has zero outlets that I can use for even L1 charging. I occasionally use free L2 charging ~1mi from my garage, but typically am driving in CS/normal mode for the last ~10 months.

Any advice on whether there should be a long term benefit to keeping the car in mountain mode (MM) to maintain a ~45% SOC vs. the ~20-30% SOC in CS/normal? My 2013 Volt with 63K miles still has experienced minimal operational (~<5%) range degradation. I believe the battery would be best served kept at the MM SOC vs. the low end normal mode. Anyone have any input? I haven't seen this specific question on optimal gas-only operation for vehicle longevity, thanks!
 
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