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Discussion Starter · #1 ·
I have just had my 2018 Clarity for a few months. Had to buy a used one because here in South Carolina I found it impossible to get a new one. Anyway I love my Clarity, but it is certainly not perfect and one of the major problems is that the computer can go crazy for no obvious reason. Maybe its stray radio waves or microwave radiation. Here's my story. From the first time I charged the car with my level 2 charger when it finished charging the charger display said 100%. Recently when the charging was complete the charger said "waiting to communicate" instead but the car was completely charged. Then yesterday after I charged it, the car refused to start and the dash was full of trouble notices brake failure, power steering problems, tire pressure monitoring problems and maybe more. I turned the power off and waited a couple of hours and tried again and nothing had changed. I disconnected the neg terminal on the 12 volt battery for several minutes and then reconnected and tried to start and it would not start. I attached a battery charger for 15-20 minutes and it started up and all the errors disappeared and the car drove fine. I took it in to the dealer this morning and they checked the 12 volt battery and it checked out perfectly, he said maybe even a little overcharged . I brought it home and attached the charger and when it finished the charger read 100% again. I'm used to having to reboot computers when any little thing goes wrong. In fact that is why you reboot computers periodically to prevent problems and keep things running smoothly. Does anyone think it is a good idea to disconnect the 12 volt periodically to prevent problems? If so I may install a cut off switch on the negative terminal to make it easy to do.
 

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I have just had my 2018 Clarity for a few months. Had to buy a used one because here in South Carolina I found it impossible to get a new one. Anyway I love my Clarity, but it is certainly not perfect and one of the major problems is that the computer can go crazy for no obvious reason. Maybe its stray radio waves or microwave radiation. Here's my story. From the first time I charged the car with my level 2 charger when it finished charging the charger display said 100%. Recently when the charging was complete the charger said "waiting to communicate" instead but the car was completely charged. Then yesterday after I charged it, the car refused to start and the dash was full of trouble notices brake failure, power steering problems, tire pressure monitoring problems and maybe more. I turned the power off and waited a couple of hours and tried again and nothing had changed. I disconnected the neg terminal on the 12 volt battery for several minutes and then reconnected and tried to start and it would not start. I attached a battery charger for 15-20 minutes and it started up and all the errors disappeared and the car drove fine. I took it in to the dealer this morning and they checked the 12 volt battery and it checked out perfectly, he said maybe even a little overcharged . I brought it home and attached the charger and when it finished the charger read 100% again. I'm used to having to reboot computers when any little thing goes wrong. In fact that is why you reboot computers periodically to prevent problems and keep things running smoothly. Does anyone think it is a good idea to disconnect the 12 volt periodically to prevent problems? If so I may install a cut off switch on the negative terminal to make it easy to do.
Where you looking where it says 100% charged? On the display somewhere, or on the HondaLink app?

If charging the 12V battery solved the problem, then most likely the 12V battery had gotten low and that's why the car was acting the way that it was until you charged the 12V battery.

If the 12V battery got low, the two most likely causes are an old worn out battery, or else something caused the 12V battery to become low. The dealer says the 12V battery checked out okay, however we don't know if they have the equipment to thoroughly check the battery, so the fact that the dealer says that the 12V battery is okay is not a proven fact.

But let's say the dealer is correct and the 12V battery is okay. In that case something caused the 12V battery to discharge. The two most common causes for that are not driving the car for a couple of weeks, but I am guessing that you drive the car almost every day. The other common cause is if someone thinks they turned on the car by pressing the power button, but they did not press the brake pedal. In that case the car is either in Accessory Mode (one button press) or ON Mode (two button presses). In both of these modes all of the power comes from the 12V battery and will eventually drain it. ON Mode looks like the car is actually running because the instrument panel is working, and the electric windows work, and the fan will run (but no heat or AC). The only real difference is that it does not say READY on the display and so you cannot drive. But sometimes people sit in their car for a long time talking on the phone etc, and if they think they are in READY mode but actually they are in ON Mode, then the 12V battery will become discharged, this can take less than an hour especially if the daytime running lights are on which they usually will be even if the headlights are not on..

Maybe none of these explanations fit your situation I am just listing some common causes.

I doubt that disconnecting the 12V battery solved the problem, and it is not normally something that you need to do on a regular basis. It can solve some problems, but the clue is that charging the battery fixed the problem which means that the problem was because the 12V battery was low for some unexplained reason. That is very unlikely to be a software error, but like I mentioned it's usually either a worn out 12V battery, or somehow it was accidentally drained.
 

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Discussion Starter · #3 ·
I don't know if their battery checking machine does a complete evaluation or not. The slip I was given shows voltage 12.61, measured 383 CCA, rated 310 CCA, Temp 78 degrees. I only had the charger on the car for 15-20 minutes and of course I drove it to the dealer. The 100% charge reading was on my charging unit. reason I mentioned that was that was what the charger displayed after charging every time it finished charging for the several months I have had the car until the last couple of charges where it finished with the display reading waiting for communication from the car. When it finished charging the day after the reset, it was back to reading 100%. which is interesting but I know doesn't prove much. When the car wouldn't start it didn't seem like the battery was discharged. All the lights including headlights were bright. If this happens again I will measure the battery voltage myself before I try anything else. All in all I'm still leaning to a computer glitch and not the battery. If it was the battery, how much does the voltage have to drop before the car would not start?
 

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I don't know if their battery checking machine does a complete evaluation or not. The slip I was given shows voltage 12.61, measured 383 CCA, rated 310 CCA, Temp 78 degrees. I only had the charger on the car for 15-20 minutes and of course I drove it to the dealer. The 100% charge reading was on my charging unit. reason I mentioned that was that was what the charger displayed after charging every time it finished charging for the several months I have had the car until the last couple of charges where it finished with the display reading waiting for communication from the car. When it finished charging the day after the reset, it was back to reading 100%. which is interesting but I know doesn't prove much. When the car wouldn't start it didn't seem like the battery was discharged. All the lights including headlights were bright. If this happens again I will measure the battery voltage myself before I try anything else. All in all I'm still leaning to a computer glitch and not the battery. If it was the battery, how much does the voltage have to drop before the car would not start?
Can't say for sure that the 12V battery is the problem, but here is some information on how things work in case it helps.

First of all the Clarity is a bit of a drama queen when the 12V battery is having problems. As mentioned even just disconnecting the 12V battery even briefly will cause all kinds of error messages to appear which seem unrelated, which go away within the first mile. And when the 12V battery is defective or near the end of its life, other seemingly unrelated error messages can appear even if the car starts and runs. So that is why we tend to cast a suspicious eye on the 12V battery whenever the car is acting strange.

If you connect a simple voltmeter to the 12V battery you probably won't be able to tell much about how much charge the 12V battery has left, as that method is not very reliable. However using a voltmeter you can see when the battery is being charged. Normally it will read just over 12 volts, but when charging it will read about 14 volts. By noticing when it is reading 12V and when it is 14 volts you should be able to observe the following charging activity:

You should see that the 12V battery is being charged whenever the car is in READY mode. The 12V battery is charged from the HV battery so the gasoline engine does not have to be running. Even if the car is just sitting in the garage, if it is in READY mode the 12V battery is being charged.

The 12V battery is also charged whenever the HV battery is being charged. However just being plugged in is not enough, it has to be actively charging the HV battery. So even if the car is plugged in while it sits for two weeks, the 12V will not be charged if the HV battery is already full. In theory you could park the car with 0 EV miles and then do a scheduled charge of one hour per day. If using level 1 and it takes say 12 hours to fully charge the HV battery, then by scheduling one hour of charging every day then the 12V battery will also be charged for an hour each day for up to 12 days. That should work anyway, I have never heard of anyone actually doing this since most people seem to use a battery tender.

Anyway maybe connect a voltmeter just to make sure that the 12V battery is being charged when it is supposed to be. It may not explain the problem that you experienced but at least it may provide a little more information about how things are working.
 

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Be carefully in the testing of the battery, fully charged is not necessarily an indication the battery is ok.

Even load tests can be excluded as valid prof the battery is ok.

Look up "sulfated car battery", the battery can act very normal and test fine, yet next moment it can be complete flat.
 

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The same thing happened to me, twice. In both cases, I had charged the Clarity overnight to full charge. I drove the Clarity, mostly in HV mode, for approx 3 hours. I stopped for gas, and when I tried to restart I got the computer malfunction cornucopia described (parking brake, tire pressure sensor, traction control, etc.) In the first case, the parking brake engaged and would not disengage, so even the tow truck was having trouble. Before going to the expense of putting the car on dollies to tow, we tried jumpstarting the Clarity. This didn't clear all of the problems, but it at least allowed us to disengage the parking brake and tow the car to the dealer. The dealer told us the same thing they told the OP: no problems with the car, the 12V battery looked fine (if anything, overcharged), they simply "reset the computer" and sent us on our way. About a month later, the exact same situation. This time, I replaced the 12V battery (OEM, but we've owned the car less than 2 years) and while numerous errors remained (including a new anti-theft error message on the touchscreen), we were able to drive it to a dealership at our destination. They are currently trying to figure out the problem; luckily I took a video of the error message display because there were no codes on the OBD2.

Frustrated that my Honda less than 2 years old has left me stranded 3 hours from home twice now.
 

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Discussion Starter · #7 ·
Did you try disconnecting the 12 volt and reconnecting. That seems to be the answer to correcting most problems. I haven't had the problem again.
 

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Yup, both times: disconnected the 12V battery for fifteen minutes. Didn't help at all. Honda dealership says everything checks out fine, but breaking down twice isn't "fine". Have to call the national office, I guess.
 

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The same thing happened to me, twice. In both cases, I had charged the Clarity overnight to full charge. I drove the Clarity, mostly in HV mode, for approx 3 hours. I stopped for gas, and when I tried to restart I got the computer malfunction cornucopia described (parking brake, tire pressure sensor, traction control, etc.) In the first case, the parking brake engaged and would not disengage, so even the tow truck was having trouble. Before going to the expense of putting the car on dollies to tow, we tried jumpstarting the Clarity. This didn't clear all of the problems, but it at least allowed us to disengage the parking brake and tow the car to the dealer. The dealer told us the same thing they told the OP: no problems with the car, the 12V battery looked fine (if anything, overcharged), they simply "reset the computer" and sent us on our way. About a month later, the exact same situation. This time, I replaced the 12V battery (OEM, but we've owned the car less than 2 years) and while numerous errors remained (including a new anti-theft error message on the touchscreen), we were able to drive it to a dealership at our destination. They are currently trying to figure out the problem; luckily I took a video of the error message display because there were no codes on the OBD2.

Frustrated that my Honda less than 2 years old has left me stranded 3 hours from home twice now.
As described in post #4 above, Clarity is known for throwing up all kinds of ominous system messages when the 12V battery is weak or even just if it was disconnected for a few minutes. And it is normal and in fact expected that you will get these messages immediately after installing a new 12V battery, but they should clear up after about a mile of driving. Did the error messages clear up by the time you arrived at the dealer?

If you had been carrying a portable jump start battery with you then you probably could have been up and running again in both situations in a matter of minutes. I started carrying one several years ago with the car that I had prior to my Clarity and it has helped me out more than once, as well as enable me to assist other people with a dead battery. The lithium versions cost around $50 but are small enough to fit in the glove box, and they don't have to be recharged as often as the larger and heavier lead acid versions.
 

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We have a Li portable jumper and tried to use it after the most recent freak-out. It didn't help, although the first time jumping the battery did let us turn off the parking brake so we could tow the car. Only could start driving after we replaced the 12V battery, and even that still had tons of error messages. They did clear up after driving a while and cycling the power.
 

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We have a Li portable jumper and tried to use it after the most recent freak-out. It didn't help, although the first time jumping the battery did let us turn off the parking brake so we could tow the car. Only could start driving after we replaced the 12V battery, and even that still had tons of error messages. They did clear up after driving a while and cycling the power.
My previous car was a 2006 Prius, and like the Clarity and really any hybrid, the 12V battery is only used to start up the electrical system and then the HV battery takes over, including starting the engine when needed. That's why the lithium jump starters are usually all that you need.

But I did run into some situations with my Prius where more power was needed, it's when my 12V battery was getting older and I tended to procrastinate on replacing it and kept using it even after it died a few times. That's because that version of Prius used a special 12V battery located in the rear cargo area, which you either got from the dealer at a very high price, or from the sole aftermarket company that made one, which was still expensive but a little less than from a dealer. Anyway I got quite a bit of experience jump starting during those periods where the 12V battery was on its last legs, as any minor mistake like leaving the dome light on would usually kill the battery. Most times the lithium battery started it up with no problem. But there were times when that didn't provide enough power and I had to use my lead acid jump starter. I carried both in the car. And there were a couple of times that the 12V battery was so dead that even the lead acid jump starter didn't work and I had to use actual jumper cables to connect to my other car. I didn't keep the jumper cables in my Prius so fortunately those two incidents occurred at home, if I was away from home I would have had to call AAA.

So I'm thinking that was your situation, the 12V was far gone, perhaps because of a defect, or if it was allowed to run down at the dealer before the car was sold, or it simply didn't last as long as it should have. For whatever reason that's possibly why your lithium battery didn't work and it required the tow truck's jump starter, or at least something stronger than your portable lithium battery. And I have a suspicion that after it was jump started by the tow truck that your car didn't need a tow. If READY appeared on the dash then you would have been able to drive it in spite of the error messages on the screen, which would have likely gone away after a mile. I realize at the moment it seemed safer to have it towed, after all a tow truck was already there, so I'm not questioning what you decided to do, I'm just saying this is such a consistent "feature" with the Clarity that after losing 12V power you will get error messages that don't go away until driving for a mile or so.

I think the error messages are legitimate in that after losing 12V power some calibrations and other data is missing and the system pops up those error messages, but as soon as you drive a short distance and the various systems are able to calibrate themselves the error messages go away. And these incidents don't store any codes in the system either which is why the dealer won't find anything wrong. As for the dealer telling you that your 12V battery was fine, they may not have had the equipment or expertise to fully test it, although even with good equipment I am told that some 12V battery problems just don't show up in a test.

Now if READY did not appear on the dash after the tow truck jump started it, or if the car wouldn't go into drive, that's another thing. But again my theory is that you could have driven the car to the dealer. Fully understand why you didn't, I'm just stating what I think the situation might have been.

Also the 12V battery is included in the 3 yr/ 36 month warranty. Of course if the dealer says the battery is fine then they aren't going to replace it for free. However I have heard of people in similar situations as yours, and after the second time the battery died the dealer was willing to replace it under warranty. So it's possible that when the second incident occurred, that instead of replacing the 12V yourself, if you had been able to jump start it or get it towed to the dealer they would have replaced the 12V for free. Of course that is all in hindsight, for the situation you were in you probably did the right thing. I'm just pointing it out for anyone else who gets into a similar situation.
 

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"Ready" never appeared on the dash, even when we could drive it (the only new message that appeared was an anti-theft message on the entertainment touchscreen). The first time it happened, we tried to drive it after jumping and it wouldn't; we could just finally turn off the parking brake. The second time, after we replaced the 12V battery, we were able to drive it but the errors didn't disappear after driving a bit. They stayed on for the entire three hours driven, and didn't clear until we turned off the car and then powered it back on.

We could have towed the car to the dealer, but we were 3 hours from home and 3 hours from our destination on a Sunday. So we would have been stuck for at least overnight, and on the hook for a hotel room. A new battery was probably cheaper :)

I'm hoping you're right and it's just the 12V battery that the first dealer missed. This particular Clarity did sit on the dealer lot for a long time before it sold, so even though I've only owned this car for less than 2 years, the battery is probably 3 years old. But if that's what it is, it's bad design to have the car react this way to a low/bad 12V battery. And in a worse scenario, I'm looking at a problem that Honda doesn't know how to diagnose or solve.

Which really sucks, because otherwise I love my Clarity PHEV.
 

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I've been driving EVs and PHEVs for over twenty years, and have been active on at least a half-dozen EVehicle fora.

The vast majority of times that these very sophisticated computers on wheels exhibit strange behaviors is because of a weak 12V PbA battery. I have always hooked mine up to a smart charger/maintainer (made to accommodate AGMs too) approximately every 60 days. No problems with strange behaviors here. When replacing the 12V battery after their warranted lifetimes, I alway put in the best AGM that I can find, that's the largest that will fit in the space.

Anecdotal? Yes, but I've seen the very obvious pattern.
 
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