[karlincolorado]

Hi all, my first post here. Recently bought a fully optioned 2015 with 16,500 miles, now 18,500 miles. The other day I was heading west up I-70 from Golden CO. I had been in Mountain Mode since Boulder and battery was at 50% or so. After a few miles heading up (this is the start of the long climb) I noticed my car would not go past 65mph while on previous trips up it had no problem going faster. I had the accelerator pegged to the floor and then there was a unexplained/sudden 1-2 second loss of power, as if I had been on cruise control and had turned that off while in Low "gear". The car was quickly decelerating, but then after 1-2 seconds, everything normalized and I had my normal power back and had no problem getting up to 75-80mph. There were no error codes or ending lights or any indication of a problem. The car has been fine since.

Does anyone have an explanation for this behavior? Thanks.

Karl

 

[rmay635703]

Switch from dual motor to single motor propulsion

 

[Barry]

Mine has never done that. The closest would be sometimes when cruising at a steady speed and then trying to accelerate suddenly to pass, it will take a second for the additional power to kick in. I think this is the switch to single motor mode mentioned above, and is common and normal for the Volt. Yours sounds like more than that. Hopefully just a glitch, but if it repeats or you notice any other unusual power issues, you may want to have it checked at the dealer.

 

[MWiener2]

I think it has to do with the altitude. The car was expecting more power from the gas motor, and it just wasn't there, so it had to change run modes.

 

[wordptom]

Hi all, my first post here. Recently bought a fully optioned 2015 with 16,500 miles, now 18,500 miles. The other day I was heading west up I-70 from Golden CO. I had been in Mountain Mode since Boulder and battery was at 50% or so. After a few miles heading up (this is the start of the long climb) I noticed my car would not go past 65mph while on previous trips up it had no problem going faster. I had the accelerator pegged to the floor and then there was a unexplained/sudden 1-2 second loss of power, as if I had been on cruise control and had turned that off while in Low "gear". The car was quickly decelerating, but then after 1-2 seconds, everything normalized and I had my normal power back and had no problem getting up to 75-80mph. There were no error codes or ending lights or any indication of a problem. The car has been fine since.

Does anyone have an explanation for this behavior? Thanks.

Karl

I’ve driven my 2012 Volt for 6+ years now, and my understanding is that the Gen 1 Volt is capable of full performance using only the single large traction motor. The smaller motor may be clutched into the drivetrain when overall efficiency is increased by doing so.

Such conditions often include driving smoothly down the road (think of conditions when cruise control is engaged). When a request for higher performance is made (e.g., by pressing down on the accelerator), split-power configuration becomes less efficient, and the car shifts back into single-motor operation. The driver may experience a slight hesitation when this happens.

In your case, you were likely driving in split-power configuration (cruising down the freeway) in Mountain Mode as you began "the start of the long climb." You then tried to accelerate, and the request for increased performance initiated a return to single-motor configuration (the observed pause).

Note your use of Mountain Mode. One often overlooked sentence in the Mountain Mode section of the manual says, "While driving in Mountain Mode, the vehicle will have less responsive acceleration."

Your experience brought to mind a comment I read a year or more ago in a thread discussing Mountain Mode, made by someone who had experienced a similar failure to accelerate as expected. This poster realized that when driving in high-demand conditions while in Mountain Mode (i.e., driving fast uphill), maintaining the battery buffer has a higher priority in the programming than providing power for aggressive acceleration.

IOW, it is possible Mountain Mode had been in the process of recharging your battery to the MM-maintained level, and you then tried to accelerate up the mountain road. Recharging that battery would have had a higher priority level than providing power for aggressive acceleration, and so your ability to accelerate as desired was limited by the computer. When the battery SOC returned to the MM-maintained level, power for more aggressive performance was again available.

 

[MWiener2]

I thought the point of MM was to keep that 20% buffer so you wouldn't run into inadequate power issues on climbs. I wouldn't expect battery charging to become a priority until it got near 0%.

Maybe his charge was getting near the 20% buffer zone or the high power demand made the gas motor kick on and that's what caused the hesitation.


How cold was it outside?

 

[wordptom]

I thought the point of MM was to keep that 20% buffer so you wouldn't run into inadequate power issues on climbs. I wouldn't expect battery charging to become a priority until it got near 0%.

Maybe his charge was getting near the 20% buffer zone or the high power demand made the gas motor kick on and that's what caused the hesitation.

In Extended Range Mode, Mountain Mode, in effect, is invoked to increase the state of charge at which the "switch to gas" takes place. The larger buffer of "borrowable" power helps prevent Propulsion Power Reduced episodes when high power demand conditions are anticipated. MM’s other "feature" is to allow the car to self-charge the battery, if needed, to the MM-maintained level (~4 bars for the Gen 1, ~2 bars for the Gen 2) so you don’t need to stop and recharge from the wall before heading into the mountains.

The OP’s 2015 Volt was starting a long climb at 65 mph, the ICE was running to generate power for the motor, and, I suspect, a bit of battery power had been borrowed during the start of the uphill climb. The SOC was nowhere near 0%, but it was below the ~4 bar level, so the ICE was also running to recharge the battery back up to that MM level. When the OP tried to floor the accelerator, the car’s failure to rapidly increase speed beyond 65 mph was less than expected (i.e., "in MM the car has less responsive acceleration") and then the car switched from split-power to one-motor configuration (the momentary hesitation).

It would appear that when driving in MM, recharging a buffer that has fallen below the MM-maintained level is a higher priority than filling power demands for aggressive acceleration (which may deplete the buffer even further).

 

[Qinsp]

It's normal, and a side effect of being more EV than Hybrid. If I'm going on long trips, I'm running Hold most the time. I use Mountain only when my battery is depleted and I know I will be approaching a grade.

Why Mountain?

The Volt works on buffering. The electric drivetrain is capable of 149HP which is adequate for the Gen 1's ~4,000lb even uphill at altitude.

But what if the battery is 'empty'? The gas motor is naturally aspirated and only 84HP. That would suck. Luckily the battery is not empty. When the gauge reads zero, there is still battery left. So the Volt adds electric power to augment the 84HP to get full rated 149HP. But the buffer is not unlimited. It will run out on grades. So GM's plan was Mountain Mode. By charging the battery up to 20% before climbing a grade, the buffer is now big enough to climb pretty much all grades.

You caught an area where Mountain is not intended to be used. It won't hurt anything, but Mountain focuses on charging the battery for an upcoming grade, not the grade you are already climbing.

The 2016+ was completely reworked. Every item was looked at, including grades. They shaved 250lb off the car, increased the battery size, and boosted both the electric power (now 120kW=161HP), and the gas power = 101HP of higher compression, less effected by altitude.

So the Gen 1 is good by hybrid standards on grades, but the Gen 2 is great. On Hold, you can go pretty far up a 6% grade at 100mph before it fades. Not a lot of 'economy' cars will hang with it on shorter steep grades.

 

[karlincolorado]

You caught an area where Mountain is not intended to be used. It won't hurt anything, but Mountain focuses on charging the battery for an upcoming grade, not the grade you are already climbing.

You are saying to turn off mountain mode when on a long grade and only use it prior to the grade? I thought MM is supposed to be used prior and during a long uphill i.e. Rocky Mountains.

 

[karlincolorado]

Mine has never done that. I think this is the switch to single motor mode mentioned above, and is common and normal for the Volt. Yours sounds like more than that. Hopefully just a glitch

Thanks, it has not happened again. Hopefully a "glitch"!

 

[karlincolorado]

In Extended Range Mode, Mountain Mode, in effect, is invoked to increase the state of charge at which the "switch to gas" takes place. The larger buffer of "borrowable" power helps prevent Propulsion Power Reduced episodes when high power demand conditions are anticipated. MM’s other "feature" is to allow the car to self-charge the battery, if needed, to the MM-maintained level (~4 bars for the Gen 1, ~2 bars for the Gen 2) so you don’t need to stop and recharge from the wall before heading into the mountains.

The OP’s 2015 Volt was starting a long climb at 65 mph, the ICE was running to generate power for the motor, and, I suspect, a bit of battery power had been borrowed during the start of the uphill climb. The SOC was nowhere near 0%, but it was below the ~4 bar level, so the ICE was also running to recharge the battery back up to that MM level. When the OP tried to floor the accelerator, the car’s failure to rapidly increase speed beyond 65 mph was less than expected (i.e., "in MM the car has less responsive acceleration") and then the car switched from split-power to one-motor configuration (the momentary hesitation).

It would appear that when driving in MM, recharging a buffer that has fallen below the MM-maintained level is a higher priority than filling power demands for aggressive acceleration (which may deplete the buffer even further).

I know MM results in less acceleration as that's in the manual. So having a tough time to get above 65mph up the Rockies while in MM was not a surprise (but I had not experienced before). My post was more about the momentary lapse of power completely, i.e., the car was decelerating rapidly for a second or two before resuming normal, i.e., faster acceleration beyond 65mph. It's the loss of power that was my concern, but no errors.

 

[karlincolorado]

\How cold was it outside?

About 35º to 40º at this point.

 

[karlincolorado]

I’ve driven my 2012 Volt for 6+ years now, and my understanding is that the Gen 1 Volt is capable of full performance using only the single large traction motor. The smaller motor may be clutched into the drivetrain when overall efficiency is increased by doing so.

Such conditions often include driving smoothly down the road (think of conditions when cruise control is engaged). When a request for higher performance is made (e.g., by pressing down on the accelerator), split-power configuration becomes less efficient, and the car shifts back into single-motor operation. The driver may experience a slight hesitation when this happens.

In your case, you were likely driving in split-power configuration (cruising down the freeway) in Mountain Mode as you began "the start of the long climb." You then tried to accelerate, and the request for increased performance initiated a return to single-motor configuration (the observed pause).

Note your use of Mountain Mode. One often overlooked sentence in the Mountain Mode section of the manual says, "While driving in Mountain Mode, the vehicle will have less responsive acceleration."

Your experience brought to mind a comment I read a year or more ago in a thread discussing Mountain Mode, made by someone who had experienced a similar failure to accelerate as expected. This poster realized that when driving in high-demand conditions while in Mountain Mode (i.e., driving fast uphill), maintaining the battery buffer has a higher priority in the programming than providing power for aggressive acceleration.

IOW, it is possible Mountain Mode had been in the process of recharging your battery to the MM-maintained level, and you then tried to accelerate up the mountain road. Recharging that battery would have had a higher priority level than providing power for aggressive acceleration, and so your ability to accelerate as desired was limited by the computer. When the battery SOC returned to the MM-maintained level, power for more aggressive performance was again available.

Thanks. I understand and expect slower performance in Mountain Mode. The concern was the deceleration episode that lasted 1-2 seconds before things normalized.

 

[Qinsp]

You are saying to turn off mountain mode when on a long grade and only use it prior to the grade? I thought MM is supposed to be used prior and during a long uphill i.e. Rocky Mountains.

I used Mountain to increase the buffer when the battery was under 20% prior to the grades. Which never happened too much since I'd run in Hold mode on such trips. I was never too attached to Mountain.

Did you ever get "Reduced Power" message? If so, then you have depleted your entire buffer.

I've only went up the I-70 when towing using a turbo diesel. That works great. Our grades peak out at about 4500' gain here.

Next time you might try this experiment: Stay in Hold (>90% battery) until the base of the grade, then switch to Normal. Now you have full EV power and your battery + your buffer. When you crest the pass, if you are under 20%, switch to Mountain to refill your buffer.

It will take some experimentation to achieve your best climbing rate. Just note the real power is in the EV drive which relies on the battery level.

There has been a lot of discussions about what Mountain can and cannot do. My 'wish' for it would have been for it charge the battery until the battery is full. Hence why I think Hold is the better tactic. But Wish List stuff is now off the table.

I just upgraded by daughter's 2013 to a 2017, and she noticed a huge difference on climbing performance.

Sidebar - One thing I did notice about I-70 is that at the higher altitudes the cooling system on all vehicles loses effectiveness. Just something to keep in mind when running WOT. Heck, I ran my transmission hot on diesel pickup towing heavy by using turbo/transmission braking heading down through Vail, and it was raining. Downhill overheating? Yup.