Engine turns on randomly in EV mode

Were you on a steep downhill at that time? If so, about what slope %?

 

I wasn't first but once I could reproduce it, I helped measure the limits.

Bob Wilson

 

prime does not have a strict ev mode like volt

 

Doesn't the manual give a list of potential reasons for the the car to exit EV mode, or I'm thinking of the non-plug one for EV operation?

 

PriusChat supplies the missing Appendix and performance, mph vs MPG charts.

Bob Wilson

 

I have 5500 miles on mine and the only time the ice comes on is when I run the traction battery down or I put it in HV mode.

 

Was the front defroster engaged?

In the following situations the gasoline engine may operate in order to exhaust heat from the engine coolant via the heater even in EV mode.
• The outside temperature is extremely low
• is operating

 

My observations, the ICE will engage even in EV only mode:
1) using front defroster only (not the dual defrost and foot) when outside temperature is cold, around less than 10C
2) downhill and using regen braking to slow down if Traction Battery at 90%+
3) long downhill using regen braking, when the energy produced from regen exceeds the Traction Battery charge rate

 

The downhill engine-on situation is very frustrating. My commute is 26.1 miles in hilly terrain. In the summer and fall (no AC and no heat) I can drive all EV from my house to work with 8 to 17 miles remaining on the battery. The last three miles is mostly downhill at a steady grade. I can add three or four miles of regen during that last downhill.
Now the frustration... As the weather has cooled to near freezing and below, I find that even with several miles of battery remaining, the ICE kicks in partway down the long hill. Why is this? I usually approach the crest of the hill at the lowest speed that traffic will safely allow - sometimes 25mph. It is four lanes (two each way), so there is room for faster cars to pass and they can slam on the brakes all they want to at the bottom where the speed slows to 35mph. I let the car gradually increase in speed until about 40mph, and then brake to keep the speed steady, or slowly reducing speed to the limit at the bottom. But in this cooler weather - again, with heat off, the ICE turns on partway down. And then it stays on for the remaining few miles until I park, wasting all that gas and having to heat the engine all the way.

I have tried going slower, going faster. Some days I have driven partway in hybrid mode so that the engine is already warmed, but the ICE still kicks on MANY (but not all) times with the temps cooler. I don't use the defroster, and usually not even the heater, and ICE still starts.

Any engineering reasons? And why does the ICE not start in the warmer temps (seemingly)? And is there anything I can do to avoid the ICE starting such as turning on some electrical accessories, braking differently, etc.?

 

We mapped it out and apparently 50F is the threshold and an SOC above 90%. Below 50F these unexpected, engine-on events become more frequent. There is a workaround.

As soon as you find a safe place, pull over and power-cycle the car. It will come back to READY in EV mode and proceed. Agreed, it is a pain. As for engineering reasons, your guess is as good as anyone else.

Bob Wilson

ps. Earlier works:

• Cold weather cruise control and unexpected engine ON | PriusChat
  
• ICE comes on anyway | PriusChat

 

Wish there was a way to force pure EV mode. I probably have the shortest commute here (7 miles one way) and even with only a couple hills, during this past winter, ICE will kick in somewhere along the commute. Mind you, this is with one or two bars of heat (not defroster) with temps never reaching below 30.

I know weather definitely plays a factor. During the summertime, I'd drive the same commute on pure EV while going 70/75 on the freeway

 

Drain the gas tank.


(although I have no idea what happens)

 

Lol. That would be an idea, but getting back home at the end of the day would be a challenge.

 

I appreciate the parameters and advice. In terms of SOC, my remaining miles is about 8 to 10 at that point, so about 30% remaining.
The power cycle that you mention may help too, although one day I had a stop at the top of the hill before the last three miles, and turned the car off. When rolling gently down the hill a few minutes later the ICE still came on. Temps were around 25F that day. So temperature seems to be the biggest factor in my observation.

These days, in the cold winter months, I now put the car in Hybrid mode when I leave the house. That way I can use the heated engine for heat and to maintain SOC for part of the first leg of the commute. I return to EV mode somewhere mid-trip, although the ICE still turns on down that hill sometimes. On the return trip, I do the same thing, using Hybrid to warm the car, then return to EV when I can arrive at home with nearly expired SOC. I register about 75mpg using this method on a 54 mile round trip.

Thanks for the responses to my question.

 

You better have a code reader handy if it's anything like my Gen3. Car (not going to say who was driving, but it wasn't me) was getting VERY low on gas and was about 1/4 mile from the house and a fully charged battery. Gave it a little too much gas and the engine tried to start and failed. This then threw a code and the car wouldn't start until the code was cleared. What a royal PITA as the reader I had wouldn't clear the particular module (for whatever reason). I ended up having to get it towed ($80) to the dealership (who charged me $150 for diagnosis). They said that I was lucky I didn't destroy the car... which I *guess* could happen if I was going fast downhill and overrevved the transmission without the ICE being able to run. Obviously we have a much smaller likely hood of that happening unless you're going over 80 when you run out of gas. Still very annoying. Ended up buying a much better code reader so that would never happen again.

 

Here is a copy from the manual:

■Gasoline engine operation in EV/EV auto mode
Even if there is a sufficient amount of electricity remaining in the hybrid battery (traction battery) and EV driving range (→P. 199, 215, 222, 239) is being displayed on the multi-information display etc., EV driving (driving using only the electric motor) may be canceled and both gasoline engine and electric motor are used depending on the situation (EV driving will be returned to automatically after EV driving becomes possible again). 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​