Engine Comes on Downhill W/O Full Charge

Did you have windshield defogger on? Here is the list from the manual that would turn ICE on.

EV driving may be canceled automatically in the following circumstances:
●When vehicle speed is more than approximately 84 mph (135 km/h).
●When power is needed temporarily, for example when the accelerator pedal is depressed firmly or when accelerating suddenly.*
●When the temperature of the hybrid system is high. The vehicle has been left in the sun, driven on a hill, driven at high speeds, etc.
●When the temperature of the hybrid system is low.
●When the heater is switched on when the outside temperature is below about 14°F (-10°C).
●When the windshield defogger switch is pressed. (→P. 491, 501)
●When the system determines that the gasoline engine needs to be started. The gasoline engine may also operate in circumstances other than those listed above, depending on conditions.
*: When traveling in the EV auto mode only

 

Welcome to the site.

You're scaring me with how much you're reading that manual. j/k

Excellent post. I'd forgotten about some of those.

 

that last bullet point is a knock down round house tko. got everything covered like my local weatherperson.

 

doesn't make sense, you're in ev, not ev auto, correct?

 

Yap, basically Toyota can program the car to turn on ICE whenever it wants to.

 

Is it affecting overall EV range and/or mpg? I have seen on my car while on EV mode with still charge left, turn off EV on uphill some times, but wasn't paying much attention, so I don't know if that happens every time the car is uphill or not. Your's is happening downhill, correct?

 

It happens to me also on a particular decent. I don't take that route often enough to identify the cause, but the first two times it happened I was in B mode and the last time I used the floor brake and it didn't happen.

Not sure.

 

is your heater temp set to 'min'?

 

What @bisco mentioned is very valid. I have had my climate control come on if my A/C is set to 74 degrees and the outside temperature is in the 60's.

Very irritating as I certainly do NOT expect my climate control to be activated unless I turn on my fan. Nonetheless, I have felt warm air flowing through my vents with the fan off and recirculate set to off. When this happens, I have to quickly set my climate control temperature settings lower as the heater chews up my battery levels.

 

While charging , if the battery is too cold , the charger will limit the current going in the Li-on Battery to avoid damaging it until the battery reach the correct temp specs.

now the speculation :
If everything is off ( defroster , etc ... ) Maybe 55 degrees is borderline for the '' Cold range '' and the ICE turn on while going downhill because the car is protecting itself from overcharging and want to limit the current going in the Li-on Battery.. the extra energy has to go somewhere .. i think the ICE start to eat it

 

If you haven't used your engine in a while or if it thinks the fuel is getting stale it might turn it on; however, I believe it gives notifications at least for the stale fuel. @Flaming's guess is probably more likely due to the conditions.

 

Use eco or ev/eco, I maintain my charge to full, even going up 1000 feet. ( I save it for the return trip )
On the next downhill portion, it’s less steep, I 80, so I lose a portion of the mpg, but still save the original charge. Now at 26, summer = 35. On the return I’ll start using EV about 20 miles out and still end up with charge left on the car at arrival. Load changes are constantly occurring, so terrain is everything.

 

Right, it is said that the engine is not really running, but simply eliminating that extra energy, ??? Other items you mention are built in load factors that quickly get normalized. If one forgets and turns the heater, defroster too high then the mpg and charge make take a big hit.

 

Today, had 20 miles of charge left, distance to home 22.2 miles, mode: ev/eco, altitude ~ 2000 feet.
Result: upon arrival 199.9 miles per gallon. Not the phoney figure that shows when starting car, but actual mpg. WHY I don’t know, the afternoon was clear and warm, that’s the only thing I can figure..........

 

Mine almost always shows that because I used no gasoline (all Ev mode). I don't see what's unusual.