This rare problem is one that we have very few first hand reports, so I didn't want to miss this opportunity which is why I had so many specific questions, so thank you for providing the details that you have already.

while in the mountains of Colorado last week. From previous experience we knew when climbing mountains we needed to be sure to have plenty of battery 'back-up', and our first few days of climbing over high passes in HV mode went OK...it was a struggle for the ICE, but it got the job done. Then one day we stopped at a Post Office and forgot to put it into HV mode when we restarted it before climbing. The battery miles got all used up just as we began to climb, and suddenly we lost most of our power, with speed dropping to 20, and eventually down to 7 mph. We stopped multiple times, turned off the car, and tried to start again, but you can imagine the danger in climbing a steep mountain road with cars zipping by at 60 mph and us trying to drive on the side of the road at 7 mph. It was a loooong and stressful climb up to the pass, as you can imagine. And dangerous. We were able to get the battery charged up a bit on the downhill coast, then I was able to find a charger station before we returned over the same pass later that day. No problems the rest of the trip. It's such a helpless feeling when this happens: you can be going, and then suddenly the engine revs up to high RPMs and the 'power indicator' on the dash simultaneously drops to 0. On one hand, this was our fault, as we know how to prevent it. On the other hand, Honda really needs a fix for this.

It seems like it has to be a software issue, which makes it even more perplexing that Honda hasn't solved it. The reason I think it's a software issue is because even with an empty battery the engine can provide approximate 100 horsepower via the generator, which although that's very weak for a 4,000 lb car it should still at least be functional. Also I have never heard of someone in this situation having no power, i.e the car comes to a stop and will not move, instead all of the reports that I have ever read including yours the speed drops below 20 for example, or 7 in your case going uphill, but there is still power. Just to confirm, on the power display your needle was exactly at the 270 degree mark? In normal driving when the needle is above that mark there is power, below that mark it is doing regen, and exactly on the mark you are coasting. In normal driving if you take your foot off the pedal the needle will drop below center because of regen, until you get below about 5 mph then regen stops and the needle goes to center just prior to coming to a final stop. Also while coming to a stop sometimes I want to coast farther so I press the accelerator pedal slightly to stop the regen, if I hold the needle at center then it is coasting almost like being in neutral. Anyway do you remember if the needle was exactly at 270 or was it maybe slightly above?

Either way it sounds like when this problem occurs the car has gone into some type of limp mode, which a lot of cars do when there is a major problem that can lead to damage to the powertrain, but they give you enough power to at least move off the road and get to safety. My theory is that a software glitch causes the system to mistakenly think there is a problem that requires limp mode. But unfortunately this software glitch doesn't seem to leave any codes in the computer for a technician to view later, which is also why people with the problem don't seem to get any warning messages on the display. Also turning the car off and on again usually fixes it so that seems to prove that there is no actual problem with the powertrain. Although your latest experience is less common where turning the car off and on again didn't solve it, even temporarily.

One thing you might try if it happens again is switching to HV Charge mode. I say this only because people have reported that HV Charge works differently than normal HV, it's more than just the expected extra RPM's to charge the battery, but other slightly different behaviors, to the point that some people drive in HV Charge all the time instead of HV. There is a slight possibility that the software glitch does not occur in HV Charge, not by design, but assuming the software glitch is a typical software bug where an oversight in the programming causes problems in certain exact scenarios, maybe by some luck that buggy piece of code is not in the HV Charge routine.

Also if you ever accidentally let the EV miles get to 0 (which is easy to do) you can use HV Charge to get just over 50% charge on the battery. Of course ideally you would realize that you are in this situation when you are still far enough away from the mountain that HV Charge has enough time to recharge the battery.

One more thing, have you ever done a 12V reboot on your Clarity? That's where you disconnect the negative terminal on the 12V battery for a minute or so then reconnect it. This essentially reboots the system and has cured many an odd software problem. After doing the reboot, the next time you start the car you will get several alarming messages about VSC and TPMS etc. but that is normal and those message go away after about a mile of driving. The 12V reboot also occurs if you replace the 12V battery since of course it has to be disconnected, or if you accidently let the 12V battery discharge requiring a jump start. So if you have had either of those happen since you have owned the car then you have already done the 12V reboot, but if neither of those has happened since you have owned your Clarity then you may want to do it proactively sometime before your next venture into the mountains.

The power supply needle was exactly at the 270 mark when the problem was happening. The RPMs dramatically go up and the power needle drops dramatically at the same time. It feels as if nearly all power to the wheels are suddenly being cut off -- as if power is suddenly being rerouted elsewhere.

Trying HV Charge mode is a good idea -- the reason I didn't think to do that is because earlier on the trip when battery charge was on 0, and we were traveling along fine on a moderate incline I put it in HV Charge mode. Surprisingly, it wouldn't charge the battery at all, even after traveling a significant distance; surprising, because typically on flat roads it's always charged the battery in HV Charge mode.

I've never rebooted the 12v battery. May give that a try. Thanks again for the tip. That's more than Honda has provided.