GM Volt Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
3,181 Posts
Discussion Starter #1
2nd Gen Volt:

Last year I noticed when the car had regenerated Mountain Mode power from an empty battery the Total Range would only show the gas range and not the gas + electric range. Yesterday I ran the tank to "Low" and this morning, with a full battery, the Total Range shows "Low" even with 55 miles showing on the electric range. It appears the software guys missed a use case in the Total Range calculation.

And for those of you wondering: The Low Fuel warning came on at 42 miles (0.9 gallons) and the "Low" came on at 0.75 gallons left. These numbers are based on the 48 MPG the car was averaging on gas at the time. The battery was depleted.
 

·
Registered
Joined
·
319 Posts
I suspect that the engineers don't want you to run out of gas even with a full battery. If you forget, or someone else drives the car after you and runs out of everything, GM wii, of course, be the first to hear about it. You could add a gallon of gas at a time if you really want to know when the total range including battery reappears.
 

·
Registered
Joined
·
1,636 Posts
2nd Gen Volt:

Last year I noticed when the car had regenerated Mountain Mode power from an empty battery the Total Range would only show the gas range and not the gas + electric range. Yesterday I ran the tank to "Low" and this morning, with a full battery, the Total Range shows "Low" even with 55 miles showing on the electric range. It appears the software guys missed a use case in the Total Range calculation.
Once you fully deplete your battery, all the grid power you put there when you last recharged from the wall is gone, and you have no more "electric range," and won’t have any more until you put some more grid power from the wall into the battery. Electric Miles = miles driven using grid power from the battery or using regen put there while driving on grid power. Total Range after depleting your battery consists only of your gas range because you have no remaining electric range.

If you use Mountain Mode to recharge the battery after it is fully depleted, it’s unclear what should happen if you switch from MM to Normal and don’t turn off the car... you have no grid power left, and the MM-recharged power was put there using gas... that power should now count as "Gas" miles and be included in the Gas range estimate. You may be able to drive battery powered miles using that MM-recharged power, but the energy usage screen should count them as Gas Miles.

If you turn your Volt off and back on again, the computer still knows you have used up all the "grid" power, but now it recognizes that the battery state of charge is above the minimum "switch to ICE" point. Now it will likely count the MM-recharged battery powered miles as Electric Miles. It most likely will NOT increase the kWh used as the power is used because it is not grid power, and this artificially increases your ev mileage (more ev miles, no additional power used) and decreases your MPGcs gas mileage (MM-created power doesn’t count as gas miles when used, reducing total gas miles without reducing total gas used).

Once you run the gas volume down to the point where the gas range shows "Low," that’s likely the only choice available to the "Total Range" display (i.e., 55 ev miles + low gas miles = ???). Keep in mind that "low" refers to the remaining volume of gas, not the range, and the actual range you could get depends on how it is used (i.e., in a cold engine for the final mile home, or in a warmed up engine cruising on the highway), making it difficult to create an estimated gas range for such a small volume.
 

·
Registered
Joined
·
3,181 Posts
Discussion Starter #4
Once you fully deplete your battery, all the grid power you put there when you last recharged from the wall is gone, and you have no more "electric range," and won’t have any more until you put some more grid power from the wall into the battery. Electric Miles = miles driven using grid power from the battery or using regen put there while driving on grid power. Total Range after depleting your battery consists only of your gas range because you have no remaining electric range.

If you use Mountain Mode to recharge the battery after it is fully depleted, it’s unclear what should happen if you switch from MM to Normal and don’t turn off the car... you have no grid power left, and the MM-recharged power was put there using gas... that power should now count as "Gas" miles and be included in the Gas range estimate. You may be able to drive battery powered miles using that MM-recharged power, but the energy usage screen should count them as Gas Miles.

If you turn your Volt off and back on again, the computer still knows you have used up all the "grid" power, but now it recognizes that the battery state of charge is above the minimum "switch to ICE" point. Now it will likely count the MM-recharged battery powered miles as Electric Miles. It most likely will NOT increase the kWh used as the power is used because it is not grid power, and this artificially increases your ev mileage (more ev miles, no additional power used) and decreases your MPGcs gas mileage (MM-created power doesn’t count as gas miles when used, reducing total gas miles without reducing total gas used).

Once you run the gas volume down to the point where the gas range shows "Low," that’s likely the only choice available to the "Total Range" display (i.e., 55 ev miles + low gas miles = ???). Keep in mind that "low" refers to the remaining volume of gas, not the range, and the actual range you could get depends on how it is used (i.e., in a cold engine for the final mile home, or in a warmed up engine cruising on the highway), making it difficult to create an estimated gas range for such a small volume.
I understand all this - I'm referring to the Trip Odometer set of displays. One of them is "Total Range" and normally it's the sum of the EV and Gas range estimates. Once the Gas Range estimate reads LOW however, the Total Range also reads "LOW" as well, even with a fully charged battery. In this case the Total Range should read the same as the EV range estimate. From a software engineering perspective, this is a missed use case in how the car can be operated.
 

·
Registered
Joined
·
312 Posts
Reports are that if it's fully charged and out of gas, it will only drive in reduced propulsion mode. All indications are that if the car is very low on fuel, complaints are the only communication it'll give. The engineers intended that the car would never be "allowed" to run out of gas.
 

·
Moderator
Joined
·
8,680 Posts
I don't know if it's still true with gen 2 and app updates, but it used to be you could still get the car's best guess in the various screens of the phone app even after the panel went to Low.
 

·
Registered
Joined
·
1,636 Posts
I understand all this - I'm referring to the Trip Odometer set of displays. One of them is "Total Range" and normally it's the sum of the EV and Gas range estimates. Once the Gas Range estimate reads LOW however, the Total Range also reads "LOW" as well, even with a fully charged battery. In this case the Total Range should read the same as the EV range estimate. From a software engineering perspective, this is a missed use case in how the car can be operated.
Yes, the driver’s display shows Total Range as the sum of EV Range and Gas Range when they both can be expressed in numbers.

You drove your Volt until the battery was depleted and then recharged via Mountain Mode. With no grid power left, you have no more ev range, so your estimated Total Range is the sum of Gas Range + 0 miles EV Range.

As a result of the MM recharging, your Gen 2 has ~2 bars of battery power. That MM-recharged battery power will enable you to drive a certain number of Gas Miles with the engine off. It is possible the estimated Gas Range/Total Range includes the MM-recharged battery powered miles.

When you have a charged battery and so little gas the Gas Range reads Low, your Total Range Estimate must include "some" gas miles, so your Total Range must be greater than the Electric Range only.

Note, however, as RePo points out, once you "run out of gas," you’ll go into Reduced Propulsion Mode. To turn this off, you must put the minimum acceptable volume of gas into the tank to avoid the Low gas message (i.e., ~1.3/1.5 gallons). By displaying a Total Range message of Low (duplicating the Gas Range message), your Volt is reminding you that you are approaching the point where your Volt may lose performance capability, so don’t try to use up the EV Range before you add more gas!

I’m not sure if anyone has ever noticed what happens to the Total Range estimate once you run out of gas. Does it then show Total Range as the sum of EV Range + 0 gas miles?

Saghost’s comment reminded me that a few years ago, during an FMM in my 2012 Volt, I still had an OnStar account that provided access to the app’s Usage Statistics. For a while after my driver’s display read Low gas range, the app did, indeed, show remaining Gas Miles and Total Miles range estimates. Then there came a point before I ran out of gas (a day or two later?), when the app stopped showing a number and would show only Low Gas Miles. I cannot remember if that point in time correlated with any particular remaining gas volume. I also can’t remember if at one point, the app’s Gas Range changed from a number to Low, but the Total Range was still a number, and then later they both read Low.

What I experienced during my first FMM was that I had been driving around town 99+% ev for most of a year (last fill up was on my way home from a vacation trip the previous year). At one point, the Gas Range display switched from 27 miles to Low. I then drove 65+ miles with the ICE running before running out of gas. And I averaged 45.6 MPGcs driving 82.08 miles while using up the final 1.8 gallons of gas in the tank. Clearly, the Gas Range estimate of 27 miles was based on the gas mileage achieved during the portion of the previous year when I mostly used gas for EMMs. Once the FMM started, I drove around with a warmed-up engine, and gas mileage skyrocketed...
 

·
Registered
Joined
·
3,181 Posts
Discussion Starter #8
I was actually at 0 miles EV range and was running on ICE alone (or as much as the Volt will do) when it went first "Low Fuel" and then "Low". The Low fuel was at about 44 miles of gas range left and the LOW was at 35 miles. My normal daily driving consumes about 11 KWh of power so I don't actually need gas.

Will there be any anticipated damage if on the day I plan to get gas I put the car in Hold Mode and just run the tank dry? If not I'll report what happens in the Gen 2.
 

·
Registered
Joined
·
2,487 Posts
There's a YouTube video where the battery was zero and they ran the tank dry, it switched to battery and ran at reduced mode for several miles to get to a gas station. Don't know why you would except as an experiment and the experiment's already been done.
 

·
Registered
Joined
·
3,181 Posts
Discussion Starter #10
There's a YouTube video where the battery was zero and they ran the tank dry, it switched to battery and ran at reduced mode for several miles to get to a gas station. Don't know why you would except as an experiment and the experiment's already been done.
That was a Gen 1 Volt. There are quite a few differences between the two generations.
 

·
Registered
Joined
·
1,636 Posts
Will there be any anticipated damage if on the day I plan to get gas I put the car in Hold Mode and just run the tank dry? If not I'll report what happens in the Gen 2.
That video seems to indicate GM engineered an "extreme emergency" battery buffer of about 4-5 electric miles at the very bottom of the allowable battery state of charge that would allow you to limp along to a near-by fuel station (most likely, a gas station), to be accessed ONLY when you run out of gas and there is NO other remaining battery power. I suspect it might still be there in the Gen 2 Volt, but I don’t know why anyone would want to demonstrate its existence.

That said, I don’t see any reason why you couldn’t put your Gen 2 Volt into Hold Mode to start the engine, then drive until you run out of gas. I would advise you have your battery charged when you do this. Some people caution against running out of gas for reasons that were of more concern some years ago regarding damage to fuel pumps, etc., which don’t apply to the Volt’s configuration.

Because of my driving habits (I try to take one annual multi-gas-tank vacation trip, but mostly ev around town), I’ve experienced 3 FMMs in the 6+ years I’ve been driving my 2012 Volt. Two of them I ended by running out of gas with my battery fully charged and ready for that moment... the access to Electric Mode returns when the engine has no more fuel, and if you have no gas, you drive in Reduced Propulsion Mode until you put at least enough gas into the tank to bring the FMM to an end (that’s enough gas in the tank to give you a gas range, not just Low).

The manuals for both Gen 1 and Gen 2 Volts say that if EMM or FMM is required and the fuel level is low, the EMM/FMM may eventually empty the fuel tank if fuel is not added. This will result in reduced, or no power. An adequate fuel level must be maintained in the vehicle to keep it operational. I’ve twice experienced the Reduced Propulsion Mode as a consequence of emptying the gas tank during an FMM, but I’ve never seen any posting indicating anyone had "no power" after they ran out of gas with some charge still in the battery. I suspect this warning is more to caution against first emptying the battery, and then emptying the gas tank.

If you do run out of gas and enter Reduced Propulsion mode, when you then add gas, the computer will perform an engine test when you first turn the Volt on again to confirm things are okay, and will then switch to battery power (if you have some charge remaining), or you can use Hold Mode and use the engine (see Out of Fuel/Engine Unavailable in the manual for full explanation).

Running out of gas actually leaves a very small amount of fuel remaining in the lines. An FMM occurs when the computer calculates the average age of the gas to be 1 year old. My next FMM following the two times I ran out of gas to end one occurred just 363 days later. The small amount of "old" gas remaining in the lines was enough to bring down the "average age" calculation for the full tank by 2 days.

During my third FMM (last Fall), I monitored the fuel volume using the Torque Pro app, and when the app reported 0 gals, 0% gas volume as I sat on a flat parking lot near the gas pumps, I started the car and drove over to the pumps (with the engine running, apparently on the fumes), and filled the tank. I then turned the car on, and no self-test was performed, as if a small enough amount of gas remained in the fuel lines to avoid the self-test. Can’t tell if that wee bit extra gas in the lines will shorten the time until my next FMM this coming Fall until it arrives.
 

·
Registered
Joined
·
2,487 Posts
That was a Gen 1 Volt. There are quite a few differences between the two generations.
I thought it was Gen 2 but it was a while ago.
 

·
Registered
Joined
·
3,181 Posts
Discussion Starter #13
Based on some of the comments about the MyChevrolet app showing total range I checked my.chevrolet.com last night. It showed 25 miles of ICE range left (85 total miles - 60 EV miles). This will almost get me to work and is a little more than I thought. I was expecting closer to 20 miles ICE range.
 

·
Registered
Joined
·
2,488 Posts
Its good to know that if you have a charge of electricity and an empty gas tank, you can still limp to a gas station. With our 2016 Volt we seldom let the gas tank go down to 1 or 2 bars remaining. Filled the tank last night and this morning our gauge is displaying 513 mile total range, 441 on gas and 72 miles on electric. It would seem one would have to try to run out of gas with all the warning systems to prevent you from doing so. Even here in the country there are only a few places where you are more than 20 miles from a gas station.
 

·
Moderator
Joined
·
8,680 Posts
That video seems to indicate GM engineered an "extreme emergency" battery buffer of about 4-5 electric miles at the very bottom of the allowable battery state of charge that would allow you to limp along to a near-by fuel station (most likely, a gas station), to be accessed ONLY when you run out of gas and there is NO other remaining battery power. I suspect it might still be there in the Gen 2 Volt, but I don’t know why anyone would want to demonstrate its existence.
I'm sure it's still there, because it isn't some special emergency buffer.

To make the car more efficient and capable of full acceleration, the car uses most of a kWh of battery as a working buffer - it brings the engine on around a kWh before the hard floor, and tries to keep most of that on hand using the engine as it matches engine rpm/cycling to road load.

When you run out of fuel, you'll generally have most of the kWh left, and that's where the three or four miles after the engine dies comes from.

On gen 1 cars, if you drive all of that and it gets stranded and you then add fuel, it'll dip below the hard floor just enough to crank the engine; I suspect gen 2 will as well but I haven't seen anyone test that.
 

·
Registered
Joined
·
1,636 Posts
I'm sure it's still there, because it isn't some special emergency buffer.

To make the car more efficient and capable of full acceleration, the car uses most of a kWh of battery as a working buffer - it brings the engine on around a kWh before the hard floor, and tries to keep most of that on hand using the engine as it matches engine rpm/cycling to road load.

When you run out of fuel, you'll generally have most of the kWh left, and that's where the three or four miles after the engine dies comes from.

On gen 1 cars, if you drive all of that and it gets stranded and you then add fuel, it'll dip below the hard floor just enough to crank the engine; I suspect gen 2 will as well but I haven't seen anyone test that.
Thanks for the explanation clarifying this is normal operation, not something special giving you access to battery power you wouldn’t have if you didn’t run out of gas. The fellow driving his 2013 Volt in the video shows us what happens, but not why.

As you point out, when you run out of gas while driving a Volt with a fully depleted battery, there’s about 1 kWh of power in the operating buffer (the power in the battery between the normal "switch to ICE and maintain this state of charge" point and the lower "hard floor" state of charge). Once the gas is gone and the engine stops, this power can be used to limp along a very few miles to a refueling station. The video shows the system also attempts to preserve as much propulsion fuel as possible by shutting down heat or a/c, etc.

One hopes the timing is such that you actually run out of gas when the buffer is full and the state of charge is closer to the normal "switch to ICE" state of charge, rather than when it is less full and closer to the hard floor state of charge.

The driver in the video didn’t seem surprised he was able to start the Volt once he added some gas after running out of gas and driving until there was no more electricity to propel the car. Once you then put gas into the tank, it shouldn’t take much power to use MGA as a starter motor to start the engine, allowing you to continue driving on gas. Is it possible there is sufficient power remaining in the battery for this purpose after the car sits for the time needed to fetch a can of gas (or to push the car to a gas pump) after you run out of gas, and you would not need to dip below the hard floor level?

Or, if there is a trigger for allowing you to use power below the hard floor level to start the engine - say, the gas cap is removed, unpressurizing the system, after you’ve run out of gas with a fully depleted battery - does the programming limit the power to the amount needed to spin MGA to start the engine? Of, if you run out of gas with a fully depleted battery, if you then "pull the trigger" and remove the gas cap, could you then replace it without adding any gas, and then drive off using battery power at or below the hard floor level?
 

·
Moderator
Joined
·
8,680 Posts
Thanks for the explanation clarifying this is normal operation, not something special giving you access to battery power you wouldn’t have if you didn’t run out of gas. The fellow driving his 2013 Volt in the video shows us what happens, but not why.

As you point out, when you run out of gas while driving a Volt with a fully depleted battery, there’s about 1 kWh of power in the operating buffer (the power in the battery between the normal "switch to ICE and maintain this state of charge" point and the lower "hard floor" state of charge). Once the gas is gone and the engine stops, this power can be used to limp along a very few miles to a refueling station. The video shows the system also attempts to preserve as much propulsion fuel as possible by shutting down heat or a/c, etc.

One hopes the timing is such that you actually run out of gas when the buffer is full and the state of charge is closer to the normal "switch to ICE" state of charge, rather than when it is less full and closer to the hard floor state of charge.

The driver in the video didn’t seem surprised he was able to start the Volt once he added some gas after running out of gas and driving until there was no more electricity to propel the car. Once you then put gas into the tank, it shouldn’t take much power to use MGA as a starter motor to start the engine, allowing you to continue driving on gas. Is it possible there is sufficient power remaining in the battery for this purpose after the car sits for the time needed to fetch a can of gas (or to push the car to a gas pump) after you run out of gas, and you would not need to dip below the hard floor level?

Or, if there is a trigger for allowing you to use power below the hard floor level to start the engine - say, the gas cap is removed, unpressurizing the system, after you’ve run out of gas with a fully depleted battery - does the programming limit the power to the amount needed to spin MGA to start the engine? Of, if you run out of gas with a fully depleted battery, if you then "pull the trigger" and remove the gas cap, could you then replace it without adding any gas, and then drive off using battery power at or below the hard floor level?
There's certainly energy left in the battery - on the 2011/2012 the hard floor was at 15% of the nominal rated state of charge (though using much of the energy below the floor will have implications for battery longevity.)

Keep in mind that the Volt runs all of the computers off of the 12V and confirms everything is happy before it closes the contactors to engage the traction pack.

I have no proof of exactly what's happening, but I think that the car authorizes power below the hard floor to crank the engine when it sees gas in the tank (won't be a significant energy usage overall - just a flicker of torque to drag the engine to 1400 rpm for a few seconds.)
 
1 - 18 of 18 Posts
Top