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Discussion Starter #1
I have had my 2017 Volt for less than 2 weeks, about 300 EV miles, and in anticipation of a long road trip this coming weekend, I decided I should run on ICE power for part of my commute to make sure the ICE worked OK.

I selected HOLD mode in my driveway before setting out, but watching the flow screen, it looked like the ICE did not kick in for a couple of minutes and about a mile of driving.

Testing again on my way home, it looked like the car stayed on battery power even while in HOLD mode until the car called for heavier acceleration, at which the flow screen showed the ICE in action.

The manual says that 3 seconds after selecting a mode, it will take effect. But either my car didn't read the manual or my understanding of what HOLD mode does was flawed. Now I am thinking that HOLD mode is intended to maintain the approximate charge level until HOLD mode is ended, but the car may use battery power in moderation and then regenerate current to recharge as it sees fit (which I would say was OK).

Anyone have any insight?
 

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Entering Hold mode and the engine actually starting are 2 separate things. If you select Hold mode and 3 seconds later the car enters Hold mode, but you happen to be sitting in your driveway at that moment, the engine won't start right away.

In my Gen 1, sometimes there is a significant delay (I'd say up to 1 minute/1 mile when cruising at slow-ish highway speeds around 60mph). But not usually. It's not particularly easy to predict nor is it clear why sometimes it starts sooner than others, but it will definitely start sooner under harder acceleration and higher power draw.

Now I am thinking that HOLD mode is intended to maintain the approximate charge level until HOLD mode is ended, but the car may use battery power in moderation and then regenerate current to recharge as it sees fit (which I would say was OK).
Exactly. That also pretty well describes how it behaves in CS mode. The engine turns on and off when the on-board computer deems it appropriate.
 

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It is working as designed. Since the ICE is usually more efficient at highway speeds, I only use Hold once I am at 50 MPH or above. The ICE will start and turn off as needed to maintain an approximate stare of charge when Hold was selected.
 

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If you look at the attached image, on the right hand side, you will notice a graph illustrating how the Volt's transmission works in charge sustaining mode.

Thus, when you are in HOLD mode, for low-to-moderate torque starts, the car will start in EV mode, and then as you increase speed and/or torque, the ICE will start and provide power.

As your driving speeds and power demands change, the transmission will shift into different modes to propel the vehicle down the road. Also, to get the most efficient point of operation, the Volt may generate excess power and put it in the battery, or take some extra power from the battery as needed.

Many times in HOLD mode, the engine will shutdown as you creep along in traffic (using some amount of the energy from the battery), and then when your speed resumes, the ICE starts and replenishes the energy taken from the battery.

The second attached image illustrates how much time the Volt's transmission spends in each mode, depending on the driving cycle.
 

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Explained well in the replies.

- Hey HAL, I want to maintain my battery SOC, so, I'm pressing 'HOLD'.
- Hello Dave. I won't respond until appropriate for the power requirements.

In other words, it's not like starting an analog engine with a key. It won't start until the computer tells it to.
 

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Discussion Starter #6
Thanks everyone for their helpful replies. Looking again at the manual, it says "After three seconds, the new drive
mode will become active."

It seems in that context "active" means something more like "the default mode", rather than that the ICE will jump into action.
 

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Another way of looking at it is to realize Hold Mode was designed to "hold" the battery at the current charge level, rather than a way to force the ICE to run. So your car's computer waits until there is a significant drop in the charge level before starting the ICE in order to bring the charge back to your "selected" level.
 

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The computer knows a secret: You can't start a cold engine and floor it.

It'll take a minute to bring it up to minimum operating temp before loading it down. Even switching on the highway- it'll take a minute before power delivery beings after startup.
 

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Thanks everyone for their helpful replies. Looking again at the manual, it says "After three seconds, the new drive mode will become active."
That's because the user interface requires that you push the same mode button multiple times to select your mode. There needs to be a delay to give you time to push the button again to scroll through the list of modes or to change your mind and start pushing the button from the beginning again. Otherwise the car would be jumping through hoops trying to keep up with you.
 

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Another way of looking at it is to realize Hold Mode was designed to "hold" the battery at the current charge level, rather than a way to force the ICE to run. So your car's computer waits until there is a significant drop in the charge level before starting the ICE in order to bring the charge back to your "selected" level.
I like this explanation.


... There needs to be a delay to give you time to push the button again to scroll through the list of modes or to change your mind and start pushing the button from the beginning again. Otherwise the car would be jumping through hoops trying to keep up with you.
I this one, too.
 

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Look at the energy screen behind the wheel, you will see when the engine start by the yellow line/level on the right side, showing power coming from the engine.

If the car is running fast enough, it will start very slow to warm up, and will only rev when warm and if needed. Then it will keep turning off or on depending on the driving and the battery state.

Basically as already stated, in hold mode the engine does not run all the time, it works with the battery and regen to maintain the battery level.
It will still use the battery when going slow or from a dead stop, then replenish the battery when the car is going faster.
 

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I selected HOLD mode in my driveway before setting out, but watching the flow screen, it looked like the ICE did not kick in for a couple of minutes and about a mile of driving.

Anyone have any insight?
Yep as everyone else said that is how it works, if you don't like how it works (for example you only have 5 miles of battery left haven't run the engine yet and you want hold to start instantly, select mountain instead, the engine will start promptly, flip back to normal then flip back to hold)

The motor will continue to run through the whole process until it warms up,

I have found on my Gen I that I can loose "hold mode" when I have 5 miles or less and select it,
so for how I use the mode it can be useful to force it to start by first selecting mountain mode.

In fact I was in hold with 5 miles remaining before I went up an actual mountain and the car went from hold to CS (normal) and then to reduced power mode.

Gen II I don't think that scenario can occur.
 

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Now I am thinking that HOLD mode is intended to maintain the approximate charge level until HOLD mode is ended, but the car may use battery power in moderation and then regenerate current to recharge as it sees fit (which I would say was OK).
One more thing, remember that the car uses State of Charge 'windows'. Rather than constantly starting and stopping to chase the *exact* set point, when you hit 'hold' it sets a lower and upper boundary centered on the SoC when you hit the button. It has to get to the lower boundary to start the engine, and get to the upper boundary to shut off.

Just like when the battery is expended. In stop and go, the engine will start, run, and shut off based on a set of logic (upper bound, lower bound, biased toward shutting the engine off at stops and only starting after you pull away, etc). But when the power gets below the lower bound, the engine runs no matter what.
 

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If the ICE is more efficient at freeway speeds, why wouldn't the ICE just kick in automatically over, say, 55 mph? Or at least have a mode for that..
 

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If the ICE is more efficient at freeway speeds, why wouldn't the ICE just kick in automatically over, say, 55 mph? Or at least have a mode for that..
The designers have to balance options and features with ease of use, but I'd love to be able to tell the car that I'm traveling 120 miles at 70 MPH and let it blend ICE and electric power.
 

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If the ICE is more efficient at freeway speeds, why wouldn't the ICE just kick in automatically over, say, 55 mph? Or at least have a mode for that..
The car doesn't know how far you are going to go. It may or may not be within the battery's range. If it is inside the battery range, EV mode is more efficient. That is the pilot's job to decide when to turn on HOLD mode.
 

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If the ICE is more efficient at freeway speeds, why wouldn't the ICE just kick in automatically over, say, 55 mph? Or at least have a mode for that..
The ICE is more efficient at highway speeds than at city speeds, but the EV mode is more efficient than the ICE at highway speeds, if you follow the difference. It's just smarter to use it at highway speeds than at the very end of the trip when you're pulling into your driveway *if you're going to run out of electric range anyway*. But that's a thing *you* know, but the car probably doesn't.
 

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The ICE is more efficient at highway speeds than at city speeds, but the EV mode is more efficient than the ICE at highway speeds, if you follow the difference. It's just smarter to use it at highway speeds than at the very end of the trip when you're pulling into your driveway *if you're going to run out of electric range anyway*. But that's a thing *you* know, but the car probably doesn't.
Seems dumb - use navigation information if a route is set, otherwise default to the way HOLD currently works :)
 
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