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Discussion Starter · #1 ·
Good Morning All,

I bought my Clarity a couple of months ago and twice have had situations where the ICE starts revving really high. Like ridiculously high for a couple of minutes. It goes away but it doesn't seem normal at all and I'm a little concerned about it.
I saw an older post about it but there were no comments on the possible cause of it or any fixes.

Any ideas?
 

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Without knowing any more about your situation, you are probably experiencing one of two things:

1. Normal higher revs common to all hybrids in certain situations
2. Abnormally high revs caused by a problem with the software (very rare)

It's hard to say which situation you are in because "ridiculously high" is subjective, and each reader of your post will likely have a different picture painted in their mind what that means, which may or may not match what you are actually experiencing. Thus the comments and advice that you receive may vary depending on how each of us interprets what you are describing.

Possibility #1, those who have never driven a hybrid before are sometimes disconcerted when the engine seems to be revving higher for no apparent reason. In gasoline cars engine revs are directly tied to how far we press the accelerator pedal, whereas in a hybrid the engine sometimes needs to charge the battery, and on its own it may at times rev higher than might be expected. The Clarity is more susceptible to higher revs when the EV range has dropped to 0. And the engine can be especially loud when climbing a long hill or mountain with 0 EV miles. But you didn't mention climbing a hill when this happened, so I assume your high revs occurred in normal driving situations. Some people say they can avoid higher revs to some extent by always have some EV range remaining when they are driving in HV mode.

However I think most people in that situation would probably choose different wording to describe it, like "the engine seems to be revving higher than normal sometimes". Whereas you used the term "ridiculously high", which again is subjective as none of us know what you experienced, but if I am imagining correctly what you experienced it doesn't seem like it's the normal higher revs situation common to Clarity, especially if it occurred while driving on level ground at steady speed with more than 0 EV miles remaining.

Which leads to possibility #2. Some early owners of 2018 Clarity said that on occasion the engine would race very fast, they used terms like "redlining" and said that it was very alarming, to the point that they found a place to pull over and turn the car off and on again, which usually fixed it. Most other Clarity owners never experienced anything that extreme. There was no known fix or software patch from Honda, and yet for some reason we almost never hear about this problem anymore. One theory is that the problem was fixed by doing a "12V reset" which is done by disconnecting the negative terminal on the 12V battery for a minute or so. This seems to clear out data and has cured various odd software issues that people experience. It can perhaps be compared to rebooting a computer, although unlike a computer, just turning the car off and on does not fully reboot the system, thus the need to disconnect the 12V battery.

Which of the two situations you experienced I have no idea, I'm just letting you know what the two main possibilities are. If what you experienced seems more like the "redlining" situation, you may want to try a 12V reset. It doesn't hurt anything to disconnect the 12V, after all whenever the battery is replaced it obviously has to be disconnected. Just so you are aware the first time you start the car after reconnecting the battery you will receive all kinds of ominous warning messages making it seem like every system on your car is failing. Believe or not this is perfectly normal, and those messages should all clear within the first mile of driving.
 

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If you do the 12V disconnect, you'll also probably lose your customized settings. Not really a "problem", but certainly a minor annoyance.
I seem to remember not that much resetting, seems like it's mostly things like mpg history is cleared (as if that had any value anyway), and the guessometer starts out a bit wacky for the first few drives until it relearns your driving habits, or at least has recent driving to calculate from which it doesn't immediately after a 12V reset. I don't think radio station presets are lost? I'm not sure though as it's been awhile. I don't think seat memory position is lost? Maybe some vehicle preferences but I don't remember, then again any settings that I never changed from default to begin with then I wouldn't know one way or the other.

Now if you do a factory reset of the infotainment system then a lot of things change, but I don't think as much after just a 12V reset. Would be nice to have a compiled list though, so that after doing a 12V reset we would know what things need to be put back the way we had it.
 

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Discussion Starter · #7 ·
Without knowing any more about your situation, you are probably experiencing one of two things:

1. Normal higher revs common to all hybrids in certain situations
2. Abnormally high revs caused by a problem with the software (very rare)

It's hard to say which situation you are in because "ridiculously high" is subjective, and each reader of your post will likely have a different picture painted in their mind what that means, which may or may not match what you are actually experiencing. Thus the comments and advice that you receive may vary depending on how each of us interprets what you are describing.

Possibility #1, those who have never driven a hybrid before are sometimes disconcerted when the engine seems to be revving higher for no apparent reason. In gasoline cars engine revs are directly tied to how far we press the accelerator pedal, whereas in a hybrid the engine sometimes needs to charge the battery, and on its own it may at times rev higher than might be expected. The Clarity is more susceptible to higher revs when the EV range has dropped to 0. And the engine can be especially loud when climbing a long hill or mountain with 0 EV miles. But you didn't mention climbing a hill when this happened, so I assume your high revs occurred in normal driving situations. Some people say they can avoid higher revs to some extent by always have some EV range remaining when they are driving in HV mode.

However I think most people in that situation would probably choose different wording to describe it, like "the engine seems to be revving higher than normal sometimes". Whereas you used the term "ridiculously high", which again is subjective as none of us know what you experienced, but if I am imagining correctly what you experienced it doesn't seem like it's the normal higher revs situation common to Clarity, especially if it occurred while driving on level ground at steady speed with more than 0 EV miles remaining.

Which leads to possibility #2. Some early owners of 2018 Clarity said that on occasion the engine would race very fast, they used terms like "redlining" and said that it was very alarming, to the point that they found a place to pull over and turn the car off and on again, which usually fixed it. Most other Clarity owners never experienced anything that extreme. There was no known fix or software patch from Honda, and yet for some reason we almost never hear about this problem anymore. One theory is that the problem was fixed by doing a "12V reset" which is done by disconnecting the negative terminal on the 12V battery for a minute or so. This seems to clear out data and has cured various odd software issues that people experience. It can perhaps be compared to rebooting a computer, although unlike a computer, just turning the car off and on does not fully reboot the system, thus the need to disconnect the 12V battery.

Which of the two situations you experienced I have no idea, I'm just letting you know what the two main possibilities are. If what you experienced seems more like the "redlining" situation, you may want to try a 12V reset. It doesn't hurt anything to disconnect the 12V, after all whenever the battery is replaced it obviously has to be disconnected. Just so you are aware the first time you start the car after reconnecting the battery you will receive all kinds of ominous warning messages making it seem like every system on your car is failing. Believe or not this is perfectly normal, and those messages should all clear within the first mile of driving.

Right, I really didn't give much info. The two times it's happened have both been when the big battery is drained and it's operating solely in hybrid mode, and it's been on level ground. I know what you're talking about with the regular higher revs that the car seems to do normally, but this is the redlining (which I would say is ridiculous for just coasting along in town, lol) It was also alarming. My wife was driving the first time it happened and pulled over and called me to say something was wrong with the car. Since she almost exclusively uses the car when it's in ev mode I just assumed that she wasn't used to the regular higher revs that it has. Then I experienced it myself yesterday. Thanks so much for your thorough answer and suggestion. I'll try that today and see what happens.
 

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Discussion Starter · #8 ·
I seem to remember not that much resetting, seems like it's mostly things like mpg history is cleared (as if that had any value anyway), and the guessometer starts out a bit wacky for the first few drives until it relearns your driving habits, or at least has recent driving to calculate from which it doesn't immediately after a 12V reset. I don't think radio station presets are lost? I'm not sure though as it's been awhile. I don't think seat memory position is lost? Maybe some vehicle preferences but I don't remember, then again any settings that I never changed from default to begin with then I wouldn't know one way or the other.

Now if you do a factory reset of the infotainment system then a lot of things change, but I don't think as much after just a 12V reset. Would be nice to have a compiled list though, so that after doing a 12V reset we would know what things need to be put back the way we had it.
After I do it I'll make a list of what I have to do again and post it.
 

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Not sure this explains your issue but it is normal for the ICE to sound like it is revving up and down when you are in HV mode and going under about 45mph. Below that speed, the ICE cannot directly drive the wheels, it is generating electricity and the electric motor is driving the wheels. It feels strange to hear the engine revving, often quite high, while the car speed is not necessarily changing speed.
 

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Discussion Starter · #10 ·
Not sure this explains your issue but it is normal for the ICE to sound like it is revving up and down when you are in HV mode and going under about 45mph. Below that speed, the ICE cannot directly drive the wheels, it is generating electricity and the electric motor is driving the wheels. It feels strange to hear the engine revving, often quite high, while the car speed is not necessarily changing speed.
Thanks Roger. Although I don't really love hearing the ICE running at all around town (it feels and sounds too rough for my liking and I avoid it at all costs, lol), these two instances have had a definite redlining, very intense sound and feel.
 

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Thanks Roger. Although I don't really love hearing the ICE running at all around town (it feels and sounds too rough for my liking and I avoid it at all costs, lol), these two instances have had a definite redlining, very intense sound and feel.
A somewhat separate topic not related to your two redlining situations, but just regarding your comment about the normal noisiness of the engine at times. There is a somewhat controversial opinion reported by several people that the engine seems to run somewhat quieter on higher octane gas. Now I realize that goes against conventional wisdom, we all expect that using higher octane than required will have no noticeable effect. Unlike using lower octane than required which can have an effect on older cars by causing knocking, but in that situation modern cars automatically retard the timing, which will result in reduced mpg and performance but there should be no noise difference. And anyway the Clarity requires 87 octane, and at least where I live that's the lowest available so going lower is not an option, only higher.

All that being said, people have reported a somewhat quieter engine running the Clarity on higher octane, and I will have to admit I am one of them that feels this may be the case. Obviously there are people who vigorously dispute that this is even possible, and say that everyone is imagining things, that's it's just a placebo effect, i.e. because people expect it to be quieter then they imagine that it is quieter when it's not. I get all of that, but since multiple people have reported this I don't think it rules out the possibility that there might be something in the Clarity software that will adjust the rpms lower in these cases.

The owners manual specifies "octane number 87 or higher required". This tells us that the minimum requirement is 87 but there is no harm to putting in higher octane. It says nothing however about increased octane having any benefit. Does that mean there never would be a noticeable difference? Maybe, maybe not. Some people say they tried higher octane and they heard no difference, which I don't doubt what their experience was. Others say they heard a difference.

I can't prove things one way or another, maybe it's a placebo, maybe it's not. But since you mentioned that you found the engine noise to be somewhat unpleasant at times, like I did (and I have been driving hybrids for nearly twenty years) I just thought I would toss it out as something you may want to try. Placebo or not, all I know is the engine sound seems less annoying since I switched. In my case I use very little gas, about three gallons a month, so the cost is minimal to keep my "placebo" habit going LOL. However if I did a lot of HV driving I would probably put up with a little more noise rather than paying for premium as that could get expensive.

I recommend before trying it, for the next couple of tankfuls pay more attention to the regular engine sounds and try and "memorize" as best you can how loud it can get at times. Then try some higher octane and see if it sounds any different to you. If it doesn't then at least you will know there is no benefit for you.

Again this is completely unrelated to your redlining situation, I was just responding to your comment about the engine noise in regular operation.
 

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A somewhat separate topic not related to your two redlining situations, but just regarding your comment about the normal noisiness of the engine at times. There is a somewhat controversial opinion reported by several people that the engine seems to run somewhat quieter on higher octane gas. Now I realize that goes against conventional wisdom, we all expect that using higher octane than required will have no noticeable effect. Unlike using lower octane than required which can have an effect on older cars by causing knocking, but in that situation modern cars automatically retard the timing, which will result in reduced mpg and performance but there should be no noise difference. And anyway the Clarity requires 87 octane, and at least where I live that's the lowest available so going lower is not an option, only higher.

All that being said, people have reported a somewhat quieter engine running the Clarity on higher octane, and I will have to admit I am one of them that feels this may be the case. Obviously there are people who vigorously dispute that this is even possible, and say that everyone is imagining things, that's it's just a placebo effect, i.e. because people expect it to be quieter then they imagine that it is quieter when it's not. I get all of that, but since multiple people have reported this I don't think it rules out the possibility that there might be something in the Clarity software that will adjust the rpms lower in these cases.

The owners manual specifies "octane number 87 or higher required". This tells us that the minimum requirement is 87 but there is no harm to putting in higher octane. It says nothing however about increased octane having any benefit. Does that mean there never would be a noticeable difference? Maybe, maybe not. Some people say they tried higher octane and they heard no difference, which I don't doubt what their experience was. Others say they heard a difference.

I can't prove things one way or another, maybe it's a placebo, maybe it's not. But since you mentioned that you found the engine noise to be somewhat unpleasant at times, like I did (and I have been driving hybrids for nearly twenty years) I just thought I would toss it out as something you may want to try. Placebo or not, all I know is the engine sound seems less annoying since I switched. In my case I use very little gas, about three gallons a month, so the cost is minimal to keep my "placebo" habit going LOL. However if I did a lot of HV driving I would probably put up with a little more noise rather than paying for premium as that could get expensive.

I recommend before trying it, for the next couple of tankfuls pay more attention to the regular engine sounds and try and "memorize" as best you can how loud it can get at times. Then try some higher octane and see if it sounds any different to you. If it doesn't then at least you will know there is no benefit for you.

Again this is completely unrelated to your redlining situation, I was just responding to your comment about the engine noise in regular operation.
It is true that higher octane gas actually burns slower so maybe the overall effect of that is a slightly quieter engine.
 

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It is true that higher octane gas actually burns slower so maybe the overall effect of that is a slightly quieter engine.
I don't think higher octane fuel burns slower per se, it just doesn't self-ignite as easily when compressed. But yes the end result of that could affect how fast or slow the fuel burns in various conditions. Either way it's not something experienced in other cars, at least not that I know of. Which is why I suggested that if the effect does exist in the Clarity it may have something to do with how the software runs the engine. In normal cars the rpm's are directly controlled by the driver. In a hybrid the computer controls rpm based on the current and predicted needs of the car and battery. The theory would be that if the computer detects a difference in fuel burn, in some cases that might affect the rpms selected by the computer.
 

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Discussion Starter · #14 ·
I don't think higher octane fuel burns slower per se, it just doesn't self-ignite as easily when compressed. But yes the end result of that could affect how fast or slow the fuel burns in various conditions. Either way it's not something experienced in other cars, at least not that I know of. Which is why I suggested that if the effect does exist in the Clarity it may have something to do with how the software runs the engine. In normal cars the rpm's are directly controlled by the driver. In a hybrid the computer controls rpm based on the current and predicted needs of the car and battery. The theory would be that if the computer detects a difference in fuel burn, in some cases that might affect the rpms selected by the computer.

I was actually thinking of doing that anyway. I'm willing to try it for sure. This is my first hybrid of any kind, let alone a plug in hybrid, and I'm still getting used to the engine droning the way it does when it doesn't seem like it would need to rev the way it does in certain situations. I've read the engine is just acting more like a generator for the electric motor so it revs differently than a regular engine. Which I can definitely get used to but the noise and vibration of it really annoys me. I'm gonna put some premium in it the next time I fuel up. Like you said for the few times I actually put fuel in it the extra cost could be very worth it. Thanks for the reply and the suggestion!
 

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I was actually thinking of doing that anyway. I'm willing to try it for sure. This is my first hybrid of any kind, let alone a plug in hybrid, and I'm still getting used to the engine droning the way it does when it doesn't seem like it would need to rev the way it does in certain situations. I've read the engine is just acting more like a generator for the electric motor so it revs differently than a regular engine. Which I can definitely get used to but the noise and vibration of it really annoys me. I'm gonna put some premium in it the next time I fuel up. Like you said for the few times I actually put fuel in it the extra cost could be very worth it. Thanks for the reply and the suggestion!
Some of the noise comes from the fact that hybrids typically use a type of engine called Atkinson cycle. You can look up the details but basically this type of engine has a longer compression stroke which is more efficient. However this design is also noisier, and thus not used on regular gasoline cars. That's probably the roughness that you are hearing. But in a hybrid the gas engine doesn't work as hard since there is an electric motor and battery to provide additional power when needed, so in most driving situations the additional noise from the Atkinson design isn't objectionable.

During times when the battery is not needed (like steady cruising) the gas engine recharges the battery. This means the gas engine has to operate at slightly higher rpm then it normally would, since at this point the gas engine is not only providing power for the wheels but also additional power to charge the battery. The computer tries to do this as unobtrusively as possible, so normally you don't notice it. But there are times when it gets behind the curve and the battery is getting too far below the level the car wants to keep it at, in that case the charging rate is increased, which means higher rpm and more noise. This can happen even when you have plenty of EV miles, that's because in HV mode it's avoiding using up those stored miles and instead tries to keep the battery at the same level that it was when you switched to HV. Thus higher rpm's at times when it doesn't seem to make sense from a driving point of view, but it's because the battery needs some charging.

Although when you have some EV miles the computer seems to realize that it has this additional charge to "borrow" from so it normally is a little less aggressive trying to keep the charge at the same level. But when you have 0 EV miles then the computer gets a bit more determined to keep the battery level from dropping much farther, so the rpms can get higher in that situation. This especially happens when accelerating with 0 EV miles, because while we may know that the acceleration is only going to last for a few seconds, the computer doesn't know that, as far as it knows you may have just started to climb Pikes Peak. So it may run the rpms a bit higher than we like to hear, even though it may not have really been necessary. In theory in the future cars will have 3D maps that are used with the GPS so that the car knows what's up ahead. But until then the computer just tries to make the best guess that it can, based on what is happening at the moment.
 

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I don't think higher octane fuel burns slower per se, it just doesn't self-ignite as easily when compressed. But yes the end result of that could affect how fast or slow the fuel burns in various conditions. Either way it's not something experienced in other cars, at least not that I know of. Which is why I suggested that if the effect does exist in the Clarity it may have something to do with how the software runs the engine. In normal cars the rpm's are directly controlled by the driver. In a hybrid the computer controls rpm based on the current and predicted needs of the car and battery. The theory would be that if the computer detects a difference in fuel burn, in some cases that might affect the rpms selected by the computer.
Yes, higher octane fuel definitely burns more slowly and evenly. That is why to get maximum efficiency from premium fuel, the spark timing must be advanced more than with regular fuel. Think about it, advancing the spark starts the fuel burn process earlier because it takes longer. With a longer burn process the fuel is burned more evenly and the energy is released more gradually. It takes more energy to ignite the slower-burning fuel and thus it is less susceptible to self-igniting under higher compression.

A rough analogy could be made to burning wood. Dryer wood is easier to ignite and burns more quickly than wood that has a higher moisture content. A similarity exists with gasoline. Lower octane fuel ignites more easily, is less stable, and burns more quickly than higher octane fuel.
 

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Some of the noise comes from the fact that hybrids typically use a type of engine called Atkinson cycle. You can look up the details but basically this type of engine has a longer compression stroke which is more efficient.
Do a little research on this. It is not the compression stroke which is longer in the Atkinson cycle engine. Taking longer to compress the fuel/air mixture would have little or no impact on efficiency. It is the expansion or power stroke which is longer. From Wikipedia: “The common thread throughout Atkinson's designs is that the engines have an expansion stroke that is longer than the compression stroke, and by this method the engine achieves greater thermal efficiency than a traditional piston engine.”
 

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Do a little research on this. It is not the compression stroke which is longer in the Atkinson cycle engine. Taking longer to compress the fuel/air mixture would have little or no impact on efficiency. It is the expansion or power stroke which is longer. From Wikipedia: “The common thread throughout Atkinson's designs is that the engines have an expansion stroke that is longer than the compression stroke, and by this method the engine achieves greater thermal efficiency than a traditional piston engine.”
Thanks, I was going from memory on that which is why I suggested they look up the details.

Do a little research on this
Don't have to, you already did! :)
 

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I came across something interesting in the owners manual in the section about the Maintenance Minder, where it says:

"Adjust the valves during services A, 0, 1, 2, or 3 if they are noisy."

I have never heard of anyone saying that their Clarity had noisy valves, or that they had their valves adjusted and the engine is now quieter. I am guessing this is something more relevant later in the car's life after a lot of HV miles. Most owners seem to be below 50,000 miles, with a large percentage of that in EV, although some have more miles than that already.
 

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I came across something interesting in the owners manual in the section about the Maintenance Minder, where it says:

"Adjust the valves during services A, 0, 1, 2, or 3 if they are noisy."

I have never heard of anyone saying that their Clarity had noisy valves, or that they had their valves adjusted and the engine is now quieter. I am guessing this is something more relevant later in the car's life after a lot of HV miles. Most owners seem to be below 50,000 miles, with a large percentage of that in EV, although some have more miles than that already.
Interesting! Any significant valve clatter is often noticeable, and usually pretty easy to diagnose by ear. If my brother's car is any indication (and if anyone wants to hear what it sounds like), stand next to a Mercedes Benz when it's cold-started. It takes a few seconds for the lifters to pressurize, and they clatter like crazy. It's not that uncommon in other vehicles as well.

So far, I've heard no indications of valve train noise in my Clarity. That the owner's manual specifically mentions it is somewhat puzzling, and a bit alarming. I'll be listening for it, in the future. This makes my installing of the engine hour meter even more important.

Thanks!
 
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