EV mode not allowed when battery is full - green bars on display: why this?

I can get to EV mode when I have 7 green bars on the display, as long as the temp of the battery pack is below the limits of EV mode. For 8 green bars, I've never been able to use EV mode, but its not a big problem to me, the Prius is going to preferentially use more energy from the pack to drain it down to a more comfortable level. The only reason I can thing of for why it won't allow you to enable EV mode with the button is so that it can burn off excess energy if it needs to by spinning the ICE.

 

Engine Warm Up.

The Prius is a hybrid. Most people focus on it's ability to save fuel. But part of it's design function is also to be a low emissions vehicle. Which is why one of the parameters for EV is the engine being up to temp.

Basically I look at it this way, everything in a Prius is designed towards the goal of everything operating as efficiently as possible....even the gasoline engine. Which means it running at least a minimum temperature, for it's own good and the good of the catalytic converter. A cold engine is not good for emissions.

If you have fully charged or decently charged battery AND the vehicle is warmed up? It should be allowing you into EV mode.

Of course even fully possible EV mode is contingent upon some factors like speed and torque demand.

 

That's a really good question otrebor, I've often wondered the same thing. I've found that (temperature not withstanding) it will still go into EV mode at 7 bars SOC, and usually also when it's just gone to 8 bars. However once the battery is truly maxed out then EV mode is disabled.

My feeling is that it's probably a generalized "battery in distress" type issue. Perhaps a lack of refinement in the battery control algorithm, because using EV power here is usually going to be a good thing for the battery. But I suspect they decided that if any of a number of things put the battery in "distress" (eg temperature too high or SOC too low or SOC too high) then the controller simply decides that humans can no longer be trusted and manual EV operation is inhibited until the relevant variables are back in range.

I know it's annoying when you've got a crap load of battery SOC and you just want to use EV, but it insists on running the ICE at the exact time when EV mode would be most appropriate! This happens to me a lot as well. Like Prius_club said however, even with the engine running if you look at the energy monitor it's typically also trying to draw EV power as well, when it's in this state.

BTW. Note that over temperature is also a lock-out condition on manually activated EV mode. And it's not a very high temperature either. It's definitely less than the temperature at which the battery is truly in distress and starts minimizing battery usage under it's own automatic control. What I'm trying to say here is that there's a manual lock out temperature on EV, even though at that temperature normal driveability and electric operation doesn't seem to be even slightly inhibited (like it is if you get the battery truly too hot).

 

I haven't noticed this behavior on my Gen 3 yet.

I suppose it could be happening and I simply haven't noticed it. I know I have been in EV mode with the battery showing near a full charge. Maybe only 1 or 2 lines from the full battery display.

Hmm...maybe I misunderstood the OP's situation and I'll have to pay closer attention to what is happening when I find myself with those parameters applied.

Could it have something to do with the immediate engine torgue demand? By that I mean there is a connection, I can be in EV upwards of 45 miles per hour if the car has momentum and the pavement is flat, smooth and/or at an incline.

But I can struggle to get into EV mode, even with a full state of charge, if I'm driving up even a slight incline, on rough pavement and/or the car is trying to rapidly accelerate to gain momentum. Often at a MPH rate that is much lower.

 

I suspect that it has to do with,
* When in EV mode, operating algorithms apparently do not permit use one of the
motor/generator (M/G1?) to spin the ICE as an air pump.to reduce HV battery energy.
* In EV mode you can get regen… which could lead to an overcharge beyond the
maxed out energy condition if you immediately went down a hill.

So, no EV at 8 green bars is an HSD enforced HV battery energy limtation...
keeping in mind that the green bars represent ~40-80% of full HV battery capacity.


(This for GenII. Applicability to Gen III not known.)