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Discussion Starter #1
I don't drive in the mountains a lot, but today I was. Ran into a very concerning issues. Tried searching, nothing on topic.

Setup: Two different drives, car shut off for three hours in between. 2015 Volt. Both times on the interstate, in MM, about 40% of battery remaining, ICE running, doing about 65. With my commute, the last part of every day in on gas, on the interstate, 65-75mph, so I am used to what the car normally feels like.

Going uphill, needed to pass, floored the gas. Saw kW reading go up to about 80 and just hung there. Car not accelerating much. Not nearly what I'm used to. Managed to get around, but concerned.

On the way back, I was going uphill, MM, ICE running, 65mph, about 40% of battery remaining. Floored it, again maxed out at about 80kW, not accelerating much. Held my foot to the floor for about 10 seconds, no change.

Tapped the mode button to Normal (foot still flat to the floor). The instant it dropped to normal mode, the car surged forward and was accelerating MUCH harder, the kW jumped to 110kW, had to get off the gas pedal after just a couple seconds.

Anyone seen this? Known issue? Something wrong with my car?
I'm not happy. In the mountains, uphill is NOT the time for my car to decide that it doesn't want to give me full power.
 

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Hmm...have you ever used mountain mode before under those same conditions? The owners manual does say acceleration will be less responsive in MM...I wonder if that is what you experienced.

But the manual doesn't say anything about switching out of mountain mode before/during a climb to access full power, so perhaps what you experienced is some kind of bug. Guess we'll wait for ***.
 

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I went through mountains without first engaging mountain mode and got reduced power warning and a top speed of 25mph,

Also not being able to pass in mountains, is well not really an issue, any car that has less than 100hp doesn't do much accelerating up a mountain.

I pulled some trailers through the mountains with a 120hp 1982 diesel suburban, it too couldn't get much above 25mph.

So consider yourself lucky, the car will not allow more than about 40kw from the engine alone and that can result in very low speeds if you deplete the battery.
 

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When did you engage MM? 10 miles before the mountain or while climbing?
 

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When did you engage MM? 10 miles before the mountain or while climbing?
Steverino, the OP stated he had about 40% charge. I would assume that when he engaged MM with 40% charge would not matter: he had what MM is supposed to provide.

I think that what we need to know is whether or not MM limits the amount of power released by the battery. Anybody???
 

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I don't have a precise answer but I can tell you that when coming over the mountains back to San Diego I had plenty of power with the ELR in HOLD. Passing many vehicles which were power limited.

One puzzle mentioned above by jbakerjonathan -- and what might be bothering the OP -- is that if the battery has a SOC of 40% then moving into MM shouldn't really be any different than being in Normal. So shifting to Normal shouldn't increase the available power. That could be a bug.

If so there might be an easy workaround. I never use MM in the ELR. I use HOLD instead. Works like MM but you have much more control and, if you have a lot of climbing to do, you can reserve a lot more of the battery. Wonder whether that would change the behavior in the OP's car?
 

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Let’s simplify the scenario. You were driving your 2015 Volt in the mountains in Range Extending Mode on the freeways at 65-75 mph with no problems. You attempted to pass while driving uphill, but flooring the accelerator added speed very slowly. Without taking your foot off the accelerator, you switched to Normal. The instant the ICE turned off and the car returned to Electric Mode, the car rapidly achieved the passing speed you sought.

Perhaps while driving at 65-75 in the mountains, your car had been borrowing from the MM-maintained buffer when needed, then recharging it. Perhaps both times you sought to pass at high speed, the ICE output was both powering the car and recharging the battery to the MM-maintained level (i.e., the electric motor was not using the MM buffer charge). When you then demanded more uphill power (passing speed of 80-85 mph?) by flooring the accelerator, the ICE didn’t have that much more to give (you did actually accelerate). Perhaps flooring the accelerator under high power demand conditions doesn’t allow the MM programming to switch from recharging the battery to using it (or perhaps it does, and this was a glitch you experienced - did you try pumping the accelerator, or did you just floor it and keep it there?).

Switching to Normal would then return the car to CD mode, freeing up the existing power being "held" by MM for normal ev use, which was sufficient to provide the acceleration you sought.
 

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When working properly, and with any buffer left in the battery, the Volt has 150HP on tap. No loss of power due to altitude!!!
Non turbo gassers lose a lot of power at high altitudes.

The OP's car has an issue. That 150HP should be on tap as long as the battery is not totally depleted.
 

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Never went up a mountain, but, both '13 Volt and '14 ELR are slower in MM. IF the generator is both charging the battery and passing power to the motors. If the generator is not charging, then, it's the same as Hold or CS. The generator is o-f-f if that's the case though.

In '14 ELR, CS actually has more power than battery alone.

What happens if you drive in Hold the entire time?

Kind of sounds like it never 'shifted' into passing mode (all EV) until you selected 'normal'. Passing mode in this case being the car's clutch mode not the driver-selectable mode.
 

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Discussion Starter #10
Let’s simplify the scenario. You were driving your 2015 Volt in the mountains in Range Extending Mode on the freeways at 65-75 mph with no problems. You attempted to pass while driving uphill, but flooring the accelerator added speed very slowly. Without taking your foot off the accelerator, you switched to Normal. The instant the ICE turned off and the car returned to Electric Mode, the car rapidly achieved the passing speed you sought.
Exactly correct.
Perhaps while driving at 65-75 in the mountains, your car had been borrowing from the MM-maintained buffer when needed, then recharging it. Perhaps both times you sought to pass at high speed, the ICE output was both powering the car and recharging the battery to the MM-maintained level (i.e., the electric motor was not using the MM buffer charge).
Unlikely. I was pulling 40-50kW in cruise before stepping on the gas, with lots of yellow in the demand indicator. The car was drawing from the buffer. I'm pretty certain the car was in torque split mode, as I had been cruising at 70 for several miles prior.
Perhaps flooring the accelerator under high power demand conditions doesn’t allow the MM programming to switch from recharging the battery to using it (or perhaps it does, and this was a glitch you experienced - did you try pumping the accelerator, or did you just floor it and keep it there?).
That's exactly what I'm wondering.
I did not lift and reapply, I didn't want to confuse the powertrain.
The second time (suspecting something was up), I applied full throttle and waited, and waited, long enough to then come up with the idea of switching to EV mode, hit the Mode button, wait for it to change modes. About 10 seconds.
Switching to Normal would then return the car to CD mode, freeing up the existing power being "held" by MM for normal ev use, which was sufficient to provide the acceleration you sought.
Seems that way. Suddenly lots more power.
What happens if you drive in Hold the entire time? ... Kind of sounds like it never 'shifted' into passing mode (all EV) until you selected 'normal'. Passing mode in this case being the car's clutch mode not the driver-selectable mode.
Seems that way to me. Every day driving home, I'm in ICE mode doing 65-70 on freeway, passing cars, etc. Never, ever noticed a problem. I have used hold before, never noticed this.
Steverino, the OP stated he had about 40% charge. I would assume that when he engaged MM with 40% charge would not matter: he had what MM is supposed to provide.
Yep. Engaged MM at home prior to heading out. EV range was depleted in the flats, ICE was running before going uphill.
I think that what we need to know is whether or not MM limits the amount of power released by the battery. Anybody???
That's what I'm wondering. If there's some secondary buffer or limit to keep you from running all the way down to "Reduced Propulsion". If so, I'm unhappy that I can't get full power in the situation where you need it most, trying to pass going uphill.
 

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MM is stingy about releasing any power when it hits the minimum, leaving you with 4 cyl acceleration up a mountain. :p You're supposed to use MM to reserve power for the mountain, then switch to normal when you most need that power.

If you're going to leave it in MM all the way up the mountain, you'll still have 30% battery at the top and then with regen on the way down and eventually have to burn it off... Nothing gained.
 

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Discussion Starter #12
MM is stingy about releasing any power when it hits the minimum, leaving you with 4 cyl acceleration up a mountain. :p You're supposed to use MM to reserve power for the mountain, then switch to normal when you most need that power.

If you're going to leave it in MM all the way up the mountain, you'll still have 30% battery at the top and then with regen on the way down and eventually have to burn it off... Nothing gained.
Interesting, that's the first I've heard that. When you say "MM is stingy about releasing any power when it hits the minimum", what's the minimum? I was a bar or two down from the MM red marker.

So, it sounds I'd be better off either switching to hold at 50% (or use MM to build up charge and then switching to hold) and running that way, rather than using MM.
 

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That has nothing to do with Mountain Mode. If your battery is depleted too much, it can't tap into it for additional power to the main motor. That would happen in Hold Mode as well.

What I think you are experiencing is a throttle response issue. I've felt the same thing when mountain climbing in the Volt with MM engaged. My solution is probably not recommended, but I typically drive with cruise control engaged. I will use it to step up my speed, and it seems to respond and accelerate far faster than if I am actively on the pedal. I have no clue why, but it does.
 

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MM is stingy about releasing any power when it hits the minimum, leaving you with 4 cyl acceleration up a mountain. :p You're supposed to use MM to reserve power for the mountain, then switch to normal when you most need that power.

If you're going to leave it in MM all the way up the mountain, you'll still have 30% battery at the top and then with regen on the way down and eventually have to burn it off... Nothing gained.
That sounds wrong. MM is intended to "hold" a buffer (Wikipedia says 45%) in case it’s needed to maintain performance in high demand situations. If the ICE output is insufficient, some of the battery MM-maintained buffer will be used, and then MM’s "recharging" feature will recharge the battery to the MM-maintained level. If you switched to Normal instead on the way up the hill when you thought you might need that power, you would drop back into Electric mode, battery power would be used even if the gas generator’s output could have handled the load, and the battery power you used would never be replaced unless you switched back into MM. You should remain in MM while driving in the mountains when need for extra power to maintain performance might be anticipated.

There are three Range Extending modes, Hold, Mountain Mode, and Fully Depleted Battery. One might expect Mountain Mode’s programming to be tweaked to maximize performance under high demands conditions (e.g., driving fast up steep mountain roads). One might expect that when the battery soc has reached the programmed low point (i.e., fully depleted battery), the system operation would be tweaked to minimize any drop in soc below that minimum level. Hold mode, in contrast (once called "City Mode" because the intent was to enable the owner to preserve battery use for urban low emission zones), allows "at will" access to use of the ICE, and the mode can be switched on at any soc level.

I have yet, however, to read any documentation that suggests there are performance distinctions between these modes under any particular driving conditions. If there were, it would bring up questions, such as:

Is it possible that running in Hold mode (with the soc at the MM-maintained level) uses more (or less) gas under any particular condition (high/low torque, high/low speeds) than running in MM with a full MM buffer under the same condition (or with a fully depleted battery under those same conditions)? Is THAT why some people think using MM in a certain way will improve MPG? Will the Volt perform better when using MM while trying to pass while driving at high speed up steep mountain roads than it would if you were in Hold mode (with the soc at the same MM-maintained level)?
 

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Discussion Starter #15
That sounds wrong. MM is intended to "hold" a buffer (Wikipedia says 45%) in case it’s needed to maintain performance in high demand situations.
I agree that sounds wrong.
You should remain in MM while driving in the mountains when need for extra power to maintain performance might be anticipated.
One would think so.
One might expect Mountain Mode’s programming to be tweaked to maximize performance under high demands conditions (e.g., driving fast up steep mountain roads).
One might
I have yet, however, to read any documentation that suggests there are performance distinctions between these modes under any particular driving conditions.
I haven't either, but I have a sample size of two where full throttle acceleration in MM was far less than switching to normal.
If there were, it would bring up questions, such as: ... Will the Volt perform better when using MM while trying to pass while driving at high speed up steep mountain roads than it would if you were in Hold mode (with the soc at the same MM-maintained level)?
Agreed, which is what we're trying to figure out. Do you know of any modes or restrictions that might have resulted in less than acceptable performance in MM?
 

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The simple answer is found in the manual on page 9-24:

"While driving in Mountain Mode, the vehicle will have less responsive acceleration."

It is working as designed.
 

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Discussion Starter #17
The simple answer is found in the manual on page 9-24:
"While driving in Mountain Mode, the vehicle will have less responsive acceleration."
It is working as designed.
Hmmm.... I did look in the manual, but must have missed that.

So, the conventional wisdom here is that MM is just Hold, with a different set point. But clearly there is a difference in the way the drivetrain manages power and what it will allow the car to do.

I was driving into work today and put it in MM, and once the battery was run down to where the ICE started and the car went into torque split mode, I tried again (on flat ground). Initially, on full throttle, the car allowed itself to drop out of torque split and run up to 110kW.
I took it out of MM and ran the battery down a little more, then put it back in MM. It once again went into torque split, with the engine running faster to try to put juice back into the battery. When I floored it, it would not leave torque split mode, and power was limited to about 80-84kW.

It seems that the car is engineered to limit the amount of power it will give below a certain internal threshold. Presumably, to prevent you from putting it in MM and blasting uphill, running out the battery, and ending up in 'Reduced Propulsion' mode.

So, from now on, I will use Hold in the hills, instead of MM (unless needing to build power, as opposed to maintaining power).
 

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.....
It seems that the car is engineered to limit the amount of power it will give below a certain internal threshold. Presumably, to prevent you from putting it in MM and blasting uphill, running out the battery, and ending up in 'Reduced Propulsion' mode.
....
How strange... Not the way I would have programmed it.
When you need full power, you should have it available, imho.

The OP was just experiencing a certain 'mode'.

So HOLD is a better MM. Just select HOLD at some point when you still have ~20-50% SOC.
 

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You’ve now demonstrated that placing additional demands on the system while the MM buffer is being recharged leads to the conditions you experienced in the mountains. You’re overlooking one Hold mode scenario that can’t be duplicated on level terrain.

If MM has no programming differences from Hold mode other than establishing a particular soc hold point, then when power is used from the Hold buffer to maintain performance, it, too, will be restored using the ICE generator, and the ICE will be both fueling the motor and recharging the battery. Under such conditions (such as flooring the accelerator to pass at 80 mph or so while driving uphill when the battery buffer is being recharged), one might expect that with Hold as well as with MM, as the manual says, "the vehicle will have less responsive acceleration."
 

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Hmmm.... I did look in the manual, but must have missed that.

So, the conventional wisdom here is that MM is just Hold, with a different set point. But clearly there is a difference in the way the drivetrain manages power and what it will allow the car to do.

I was driving into work today and put it in MM, and once the battery was run down to where the ICE started and the car went into torque split mode, I tried again (on flat ground). Initially, on full throttle, the car allowed itself to drop out of torque split and run up to 110kW.
I took it out of MM and ran the battery down a little more, then put it back in MM. It once again went into torque split, with the engine running faster to try to put juice back into the battery. When I floored it, it would not leave torque split mode, and power was limited to about 80-84kW.

It seems that the car is engineered to limit the amount of power it will give below a certain internal threshold. Presumably, to prevent you from putting it in MM and blasting uphill, running out the battery, and ending up in 'Reduced Propulsion' mode.

So, from now on, I will use Hold in the hills, instead of MM (unless needing to build power, as opposed to maintaining power).
It is not specifically limiting the power. When in MM you are asking it to do multiple things. 1. Recharge the battery, 2. pass while going up the hill, 3. do it at maximum acceleration.

Keep in mind that the two electric motors together give you maximum torque. However when in MM mode (or HM as well) they must be used to restore the SOC on the battery.

That is why the manual states that if you anticipate driving in mountains to use MM before you get there in order to bring the SOC up. Then when needed return to NM for full power. If needed again you can use MM on the downhill side or on flat terrain.
 
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