Hi everyone,

I had an issue on August 23, 2020, where the car slowed down and over-revved twice. Today, I took the car to the dealer this morning, and was told (1) Honda's Diagnostic tools could not find indications that an error or an issue occurred, (2) could not replicate the problem, and (3) without a diagnostic capture of the incident the dealership could do nothing about it.

After some research today, it seemed like others may be having similar issues. How were you able to (1) resolve the issue with Honda and (2) able to help document the Computer error code so the next time it happened?

Would anyone recommend an OBD tool that can monitor in real-time what "gear" the CVT is in, engine loading, speed, temp, and other parameters that may help isolate the problem while driving?

Here is what happened below:

(1) State of the car:
Car was in HV mode with 75% of battery, and not going uphill.

(2) Symptoms:
While driving or starting from a stop, the engine sounded like it shifted into a lower gear by the loud engine revving noises it made. It occurred twice.

(2a) Occurrence 1:
While driving at 35 miles an hour, the transmission sounded like it went to a lower gear, and the car was slowing down even after pressing on the gas. What seemed to address the problem was turning off HV mode, let it go into EV mode, then put it back into HV Mode.

(2b) Occurrence 2:
Between 10 to 20 minutes later. From a full stop at a stoplight, the transmission sounded like it was stuck in a lower gear, pressing the gas did not accelerate the car past 19 miles/hour. What seemed to address the problem was turning off HV mode, let it go into EV mode, then put it back into HV Mode.

In both cases, putting the car back into EV Mode, then back in HV mode, seemed to resolve the problem of the loss of power and engine over-rev. It seems odd to me that Honda would not have a fix for this yet.

This seemed to be more common very early in Clarity production, reports like this are very rare now. What year is your Clarity, also what is the manufacture date (located on driver door jamb). How many miles on it, how long have you owned it?

Also not questioning what you experienced, but the more common issue reported (again mostly from a couple of years ago) is a very loud engine, some have described it as the engine is redlining. Based on these reports there may be some type of glitch that makes the RPM shoot up very high to an alarming level (although not harmful to the car), but most of that power is going to the battery not to the wheels, thus the sensation that the car has slipped out of gear (metaphorically as Clarity does not have gears, it doesn't even have a CVT). There is a theory that when this happens some people assume based on the sound that they are pressing the accelerator to near maximum so they don't press it any further, thus believing the car will not accelerate, when actually it would if they would have pressed the pedal farther.

Realistically it's difficult to gauge how far you are pressing the pedal, other than when the pedal is to the floor, most of us gauge accelerator pedal position by engine sounds or acceleration. So the theory again is that when people experience super excessive high RPMs, the pedal is only slightly pressed, enough to only barely maintain speed, but the high engine revs causes the driver to think they are pressing the pedal more than they really are, thus creating a sensation that the car will not accelerate.

Again not saying this was your situation, but do you remember if you tried pressing the pedal all the way to the floor? Any chance you glanced at the power gauge during this time? I understand if you didn't as an incident like this can be quite distracting, but it would be helpful if it happens again to watch the power gauge to see what it indicates during the high rev situation. In preparation you may want to watch the power gauge in normal driving perhaps more than you normally do and memorize what levels the power gauge indicates at different accelerations. Then if the incident happens again you will have something to compare it to.

As for an RPM gauge, there are relatively inexpensive OBD2 bluetooth devices that you use with a phone app. Torque Pro is a popular app, the free version will show RPM. Again it would be good to use it in regular driving and note typical RPM's, then if the incident happens again you will have something to compare to. This won't necessarily help solve it but it will give you more of a qualitative description to report to the dealer.

This does not directly respond to your issue, but this video is good background information that maybe will help visualize what might be happening under the hood when you are having this problem. If you have not seen it yet, it's a really good explanation of how the Honda PHEV drive train works in its various modes.

Problems like this that happen randomly and infrequently are a bear because it leaves no footprint and of course it never shows the problem when you take it to the shop. I wish you luck.

with our 2018 Clarity Touring a number of times the first year we owned it. Sometimes it would happen in the winter during severe cold, other times in the mountains with a fully loaded car. Very disturbing and also terribly dangerous, so I filed a formal complaint with the National Traffic Safety Board. In reference to an earlier post, pushing the accelerator pedal to the floor does no good in those situations. I took it to our local Honda dealer and they exerted a good faith effort by hooking up a computer and driving with me but we couldn't duplicate the problem -- no surprise there. I considered using our state's Lemon Law due to safety concerns, but we haven't had any problems the last 1.5 years so decided to keep it. Am heading to the mountains again in a couple weeks so will be interested to see if we encounter the same problems again. I know of no solution, other than keeping your battery as fully charged as possible whenever in HV mode.

Thanks for the detailed info. I read all of the NHTSA reports a while back and I found eighteen that described a similar complaint, car would not accelerate, slowed down to 20 mph, etc. But most of them were from a couple of years ago there were very few recent reports. When I read the reports it sounded like what you experienced, in my opinion they couldn't all be explained by the high RPM theory where drivers are misled by alarmingly high RPM's into believing the car would not accelerate. Unfortunately none of the reports that I read specifically stated that they tried pressing the pedal to the floor, so there was no way to prove this wasn't the case to those who were dismissing the reports as just new owners who didn't understand how the car works. Although perhaps coincidentally I did notice that most of the reports were from people who had only owned the car for a relatively short time. It makes me wonder if perhaps the problem was a software glitch that somehow clears up as the car is driven longer and builds up more data. Or maybe the problem was fixed in a software patch that the owner may not have been aware occurred. Just guesses as a way to explain why the problem seems to have mostly gone away.

Thank you for your responses. The respones are helpful; I'm surprised Honda has not responded to this because it seems like a life safety issue. Imagine trying to figure out why your car is slowing down on the freeway from 65 miles an hour while you press the gas, and traffic around you is still doing 65.

@2002 , Purchased the 2019 Honda Clarity in March of 2020 brand new. When it happened on 8/26, I noticed the sound first, then looked at the speedometer and saw the loss of speed from 39 miles per hour and continued to drop. I pushed the pedal a few times, and speed continue to drop. The second time was from a dead stop, I was able to get up to 19 miles an hour, and the car would not go past that. In both cases, what seemed to resolve the inability to accelerate was turn off HV mode for a moment (less than a minute), and re-enabling it again.

I'm waiting on the BlueDriving OBD-II; hopefully I can log other data should the event happen again.

@60Hertz , thank you for the link; it helps to understand this a lot better.

@lefty , It seems like the problem I'm having now. It happens when it happens, and it happened again yesterday, I took the car into the shop today, and Honda could not find anything in the codes.

@2002 , I am wondering the same thing; it seems like if this were a hardware problem there would be "codes" (smoke, sounds, etc.) but for Software I would expect an exception code for scenarios that did not meet the various use cases, unless it is an "undocumented feature" that perhaps Honda may not be aware.

Here are the details fo the occurrence on 2020/09/07 approx 3 PM.

(1) State of the car:
The car was in HV mode with 45% of battery

(2) Symptoms:
Pressed the gas and the engine revved and did not get past 12 miles per hour.

(3) Occurrence:
Driving Southbound on the 15 freeway downhill in Stop and Go traffic. I noticed the pressing the accelerator the would engine rev, and the car seemed to have trouble accelerating; this time, I unable to drive past 12 miles an hour.

Note: The 12 miles per hour is strange because I would not expect this to occur, considering the driving direction is downhill.

(4) Workarounds/What next?
What seemed to resolve the inability to accelerate was to disable HV mode, drive using electric for a bit, then turn HV Mode back on.

Took the car into the shop today, and Honda reported that there were no error codes that would indicate there was a problem and that Honda was unable to replicate the issue.

I've got a Blue OBD arriving, so I can start logging other engine parameters when this occurs. I'll share what I find the next time this happens.

So it happened to you again yesterday. While it was happening did you have a chance to glance at the power meter to see how the meter was reacting to accelerator pedal movement compared to other times? Did you try pressing the pedal to the floor? Also I realize you don't have an RPM gauge hooked up, but when the engine was revving was it louder than normal, or was it at a sound level that you hear in normal driving.

Hi 2002,

Thank you for the quick follow-up.

I heard the sound first, looked at the dash and noticed that when pressing the accelerator down I would hear the engine rev and keeping an eye on the speedometer, I noticed it did not go past 12 miles an hour wiht the pedal down. I'm not sure why, what seems to fix the issue is to disable HV mode and re-enable it after a short period of time. I do not know how long this workaround will be effective though.

To equate the noise level to a manual transmission, it sounded like being in 1st gear, and forgetting to shift into 2nd gear when you enter the main street and flooring it.

I can't wait for the BlueDriver OBD-II to arrive so I can start logging the RPMs, Torque, Engine Loading, and Temps.

I am looking at it from the point of view of a Honda technician, they can't duplicate the problem on a test drive since it is random, and they don't see any codes, so they are relying completely on you for information. Even if you gave them a readout of RPM, torque and engine load, that doesn't really help because most of the time the Clarity engine is just spinning a generator and making electricity, some of which goes to the wheels and some of which goes to the battery. So RPM etc, or even the sounds that the engine is making, does not indicate how much power is actually being delivered to the wheels by the electric motor even in normal driving. Phone apps are not going to provide that level of information.

So the only clues that you can give them are what were the power levels indicated on the display, and what was the pedal position, as accurately as you can describe them. I have brought up the power gauge but I don't know if you know what I am talking about as you haven't mentioned it. There is a semi-circle that goes around the speedometer. Most critical to this discussion, the pointer starts out positioned at the left side of the circle when no power is going to the wheels. In normal driving as you press the accelerator the pointer begins to move around the circle. I mentioned before that you should observe how this pointer moves during normal driving, and how it relates to both pedal position and acceleration. I would pay specific attention to how far the pointer moves at various accelerations and at various cruising speeds in normal driving. It does not have numerical markings, but it does have eight "notches" around the circle. As you observe the pointer in routine driving you will see that the pointer is pretty consistent as to how many notches it moves at various accelerations and cruising speeds. I really think you should make these observations during normal driving, and then if the problem occurs again, I realize it's natural to focus on the speedometer, and I realize in traffic there is a stress to quickly solve the problem, but if there is any way possible while you are looking at the speedometer to also look at the pointer on the power circle and see where it is positioned and how it responds to accelerator pedal movement. This is the only gauge that shows power going to the wheels and thus in a loss of power situation it is an important gauge to look at.

A Honda technician will also want to know how far you are pressing the pedal. The problem is that this is completely subjective to describe, it is very difficult to communicate how far you are pressing the pedal. With one exception, pressing the pedal to the floor is about as unambiguous as you can get, i.e. you are pressing the pedal until it will not physically go any farther. I asked you if you tried pressing it to the floor, you said you pressed it down, but I don't know what that means, and neither would a Honda technician. Again I have no reason to question anything you are saying, I am just pointing out that from a technicians point of view, they need specifics, the more you can provide the better.

Actually the Clarity is unique because it has another unambiguous point in pedal travel which is the detent. I am not sure if you know what this is as I have not heard you mention it. The detent is a click that you can feel in the pedal when you are pressing the pedal nearly to the floor but not quite. It is designed mainly for driving in Eco mode where the detent is the point where the engine will come on in EV mode. In Normal and Sport modes the accelerator pedal is mapped differently so the detent does not really mean anything in those modes. But the important thing for your situation is that the detent provides another unambiguous indication of how far you are pressing the pedal which you can communicate to the technician. I recommend that in normal driving that you press the pedal to the detent to get used to how it feels when you go past it, and then if the incident occurs again as you press the pedal you will be able to recognize if you are going past the detent.

Ideally you could then tell the Honda technician something like this, "I pressed the accelerator pedal but the car would not accelerate. I could feel that I had pressed past the detent, and I continued to press the pedal all the way to the floor until it would not go any further. With the pedal to the floor the power indicator on the display did not even go to the first notch, and the speed would not go above 15 mph even though I was on level ground". This type of specific information will be invaluable to anyone trying to understand and troubleshoot the problem, as it removes subjectivity and ambiguity.

You may even want to consider mounting a video camera pointed at the display. Obviously that will result in mostly unusable footage that has to be discarded, but ideally the camera will be running (with sound) if the incident occurs again. It will show the power gauge, and the audio should pick up the engine sounds since you say it is very loud. And during the incident you should also give verbal commentary about where the pedal is positioned, i.e. "I am increasing pedal pressure. I just felt the detent and I have gone past it. I now have the pedal pressed completely to the floor". If you had a video like this that you could show to a technician it would go a long way towards getting them to escalate it to Honda technical.

@2002 , Thank you for the in-depth explanation. I'll make sure to include those observations for the next time it happens. It is helpful and useful information.

Thank you!