ICE runs after going down a hill at the beginning of my drive.

Is that a new error code showing up on your car?

 

I topped off my battery yesterday and then went down a long hill. I only used the foot brake. During the entire time the energy meter did not dip into the green at all, nor did the engine start. Basically when the battery is full, avoid the regen paddles until you use up some battery.

 

Are you able to experience repeatable results with your experiment? Does the engine always start if you touch the left paddle at the top of the hill after you top off your battery?

 

It was a joke. Look at it closely.

 

Drum roll please...we have an answer!



At around 21:10 Alex on autos explains what happens if the battery is full and you need to brake going downhill. He says that Bobcubsfan's issue is actually a brilliantly novel design of Honda so the car can still use the regen system to enhance braking without hurting the battery. As explained, the regen motor will help stop the car and the drive motor will turn the ICE to expend the energy. You are not wasting gas! In fact, this is a favorable condition if you don't normally use the ICE much for driving the car. In this mode, you keep your ICE properly lubricated without using any gas. Absolutely brilliant and Bob has been experiencing one of the benefits of driving a Clarity and not a defect. Of course, Bob can avoid it altogether by just charging to 80-90% and recapturing some of the energy he used driving up the hill and prolonging the longevity of the battery.

 

Simple question: When the ICE comes on if it is not using gasoline why does the HV range go down?

 

Hi Bob,

Well, we do know that the HV range calculator has been defective for quite some time. As you know, Honda put out an update to fix the inflation issue on the software but probably did not fix this issue.

 

Do you know for certain that gasoline is NOT being used?

 

We are so close to understanding this....! I know nothing about OBDII except what I have gathered secondhand, but would an OBD fuel consumption rate be the nearly-"gold standard"? (though even this might be fooled with a freewheeling engine).

One of the standard codes, 5E (hex) or 94 (dec), gives "Engine fuel rate L/h", according to Wikipedia. Does one of the OBD gurus know if this standard code works for our Claritys?

 

I don't know for certain but Alex on Autos is one of the most thorough car reviewers out there so it's likely that his information is coming directly from Honda. If gas does inject into the engine, either the engine will fire up (that would be counterproductive) or if it doesn't ignite, the unburned gasoline will pollute and cause all sorts of problems like ruining the engine oil and potentially causing backfiring in the exhaust system when the ICE next fires up. Neither scenario is likely. The fuel injection is computer controlled so it is a simple thing for the gas to be shut off.

 

So it must be burning gasoline which still begs the question why? The Chevy Volt only does this rarely. Same technology.

 

My house is on the hill. At the morning when I going down the hill with the fully charged battery, if I don't apply the brake from beginning, the ICE will come on and I can see the white smoke in the rear of my car via the mirror so I believe the the ICE did burn gasoline.

 

Even if the HV numbers are off the fact that there is a decrease is evidence that gasoline is being burned And then there is the obvious engine noise.

 

It has to be burning gas, and two things support this. One, the HV range goes down and two, if you stop completely you can hear the engine running. It can't run if it's not using gas.

 

Exactly. And if you set the view on the main screen to see the flow of energy you will see the ICE charging the battery when you come to a complete stop even when the battery is supposedly fully charged.

 

Once ScanGauge II codes are freely available for Clarity, it will be easier to both test and monitor what is happening - both to the battery and to the system - when ICE is engaged under these conditions. On the Prius PHEV, there are conditions under which ICE runs at 960RPM, and no fuel is being expended. The bigger question here is what happens when a battery is "full" and regeneration occurs - as in starting out at "100%" and going down a hill. I can say with certainty that this ICE-on "feature" exists in the Toyota vehicle, too, and it's been bantered back and forth on Prius Chat for years - with no truly satisfying conclusions. Of course, Prius is a serial hybrid, and supposedly Clarity is not. For now, understanding the Honda system better and more completely would seemingly lead to the solution. The takeaway is that it's not an isolated incident.

https://priuschat.com/threads/full-battery-going-downhill-engine-coming-on.175975/

https://priuschat.com/threads/full-battery-downhill-engine-start-is-a-pain.105663/

 

It all comes down to whether the engine actually starts up and starts burning gasoline to use up excess electricity that the battery is too full to absorb.

We know from the SAE paper by the 3 Honda engineers that the Accord Hybrid spins the engine with the valves closed and no fuel. Clearly, the Insight is doing the same thing. However, that doesn't guarantee the heavier Clarity Plug-In Hybrid doesn't require a more aggressive way to burn off excess electricity that can't to to the fully charged battery.

As noted above, there are many posters here who know absolutely that their engine starts in response to a regen situation when the battery is fully charged.

It makes no sense that the engine would be generating even more electricity, so the starter motor/generator cannot be functioning as a generator in this situation. So the power from the traction motor has to go somewhere other than the battery. My theory is that the starter motor/generator is using up the output from the traction motor to resist the engine.

To slow the Clarity going down a long incline:

1. The traction motor, operating as a generator, sends power to the battery
2. The battery becomes fully charged
3. The starter motor/generator starts the engine
4. The starter motor/generator reverses its torque (this is the key unverified event)
5. The traction motor, still operating as a generator, sends its power to the starter motor/generator
6. The starter motor/generator uses up the power from the traction motor by resisting the engine's torque

Can anybody Ask Alex about the Clarity?

 

I would sure like to know the answer to this mysterious behavior.

 

Not so sure we have the definitive answer yet, @PHEV Newbie.
You can add another vote for the engine actually running, burning gas, and not just turning over with the valves closed like the Accord. On two such occasions, I stopped afterward and the ICE was either warm or running which tells me gas is being burned, and on both occasions my spark plug coil inductive hour meter incremented telling me the spark plugs were firing. No disrespect intended for Alex who is a great source, but I have proof my engine ran when the battery was fully charged and I went downhill or had to heavily use the brakes. I think he is mistaken on this.
We don’t know for sure yet exactly how it does this but @insightman has the best theory so far that fits all the reported facts.

 

There's an important difference with the Insight (subject of the video) and the Clarity. The Insight is a hybrid so the ICE is on most of the time and therefore, when this regen situation occurs, if Alex on Auto is correct, no gas is used in that moment. The engine can shut off and on as it's already warmed up. However, the problem with the Clarity is that the ICE wasn't on before the regen turns a cold ICE on. Even if no gas is used in that moment of regen, the ICE still has to warm up, and this obligatorily uses gasoline.