Help: ICE running with full battery when not in HV Mode

The Clarity PHEV has no engine-driven alternator to charge the 12-Volt battery, so the engine doesn't run unexpectedly for that purpose. Instead, the traction battery charges the 12-volt battery through a DC-to-DC converter whenever the Clarity is On or charging the traction battery from an EVSE.

 

I think you might be right. Since that idea was first introduced I don't think I have seen any evidence so far to the contrary. I have a 2018 and it happens, although rarely. It did happen a couple of weeks ago, but prior to that was probably a year or so. I have a stop light 3/10ths mile from my house, at the top of a slight grade. If the light is red I approach it fairly slowly, not to avoid the engine from coming on but there's just no reason to go faster when the light is red, especially since I'm going uphill. If it's green then of course it's not a problem. However on occasion it will turn yellow right when I am at that go/no go decision point, and when it's a no go I may have to hit the brakes a bit harder to stop in time, and that's when the engine comes on.

I agree for those of us that it doesn't happen that often, which I get the impression is most people. New owners are the most likely to comment on it, as they are understandably perplexed because it's such a bizarre phenomenon, and they are looking for an explanation. Sadly we have to inform them that even the greatest minds in the Clarity brain trust that we have here have been unable to come up with an explanation, at least not an explanation that can pass the giggle test.

I do feel sorry though for people that it happens more often. I remember one person who lived on a hill said it happens pretty much every time, I don't think even turning on the heater helped. They were pretty frustrated. Which is understandable if every time you leave your house in EV mode, no matter how short the drive, you have to put up with the engine running for the first several minutes.

I know you have a 2018 (VIN #1 I think!). If it's only 2018's that experience this that may help explain why only a few people like us seem interested in the topic, as we have gone round in circles trying to figure out what could possibly be the logic Honda had in starting the engine when using regen with a full battery. If it's truly just a 2018 "feature", then maybe after the first year the engineers came to the same conclusion that we did which is that it's a really dumb idea. Maybe in 2019 they changed it to simply use the friction brakes in these situations. Or maybe it continues to spin the cold engine but just without starting it. Although if the latter theory is true, then someone with a 2019 and later who has Car Scanner or similar should be able to verify it they see some RPM in these situations.

 

Regen braking with a full battery is a situation not well handled by the Clarity software. The workarounds I use to keep the ICE from unwanted starts:

1) Estimate time needed to reach full charge and set charge timer to something less than that, trying to ballpark about 90-95 percent charge.
2) If I know the battery is at 100 percent:
a) Crank the heater to max for a couple of minutes, sort of using it as a braking resistor. Obviously this works the best in cooler weather.
b) Shift to neutral before braking until driving far enough to pull some charge off the top of the battery.

If the ICE does get a "false start" due to braking when the battery was full, I just keep driving and it will eventually shut down on its own and return to EV mode. It can take a while in some situations.

 

That works, even though it's a bit of a hassle. But personally I would only do that if I didn't need a full charge that day. If I am driving farther I always charge to 100%. Those few minutes of engine idling will use very little gas, much less than the extra amount of gas you will use if you forfeit 5-10% of EV range just to avoid a false start.

 

That's a good point. I do the same if I know I will be driving beyond battery range. Forgot to mention in my post.

 

We have a 2019 and it will happen once in while.

 

Is there a particular stop sign or stop light where it usually happens? Or is there a hill involved?

 

Almost always the first stop after leaving a level 2 charger. Not always the same charger. My wife gets free charging at work and ICE will sometimes start at her first stop. We also get 1 hr free charging at the grocery store and the same thing happens there. Depending on temperature and preconditioning, it will happen frequently.

 

Thank you. When I started driving 2018, I had the same thing happen as the other new person in this issue. I was trying to drive 100% Electric, and the motor would turn on in the morning for a short time. Then after a year, it just stop as I was using gas at times. Finally found one member in two large groups, the other is Facebook Clarity group, that know more info.

 

I have a 2018 and it happens every now and then. I am at the top of a hill and especially in the dead of winter, when the batter is being strained anyway, the engine comes on when i leave the house. It also comes on in very cold weather if I push the heater fan up beyond 2 bars.