EV switch doesn't work in cold weather

I'm starting to come to a better understanding of the limitations of the manually forced EV mode using the EV switch on the Toyota Prius. From what I've observed in most cases the Prius DOES NOT let you know if you've successfully switched into EV mode or switched out of EV mode using the switch. Except in special cases.

If the Prius refuses to switch into EV mode than any attempt to use an EV switch is met with 3 rapid beeps. If the Prius would prefer not to go into EV mode, such as during initial engine startup, but is willing to listen to your request it gives you 1 beep.

This morning it went down to 32 deg F and when I tried to activate the EV switch instead of being met with a single beep I got a triple beep and the gas engine started up against my desire. There was no way I could force the Prius to go into EV mode at this temperature. There was no question about my EV modification being proper, because I would have never gotten this triple beep telling me my EV request was rejected.

I've also noticed that the EV switch tends to be ignored if you're foot is already on the accelerator. It's not clear that this is always the case. But it seems that you can't reliably depend upon switching on and off the forced EV mode at will.

Therefore, in cold weather you can only see practical use of the EV switch at the end of a trip for parking, or for a quick start up and move in a parking lot after the engine is already warm.

Does the above make sense to everyone?

Eh... because I have driven in stealth when the temperature was 50F degrees colder. (Yes, -18F!)

So electric drive is indeed possible (once the entire system is toasty warm), but that request to use EV is going to especially stubborn compared to that in "no jacket" weather.

No issues here either (though I've thankfully not experienced subzero weather w/ my Prius). Many an evening starting the car in 20degF out in the company parking lot.

Do you pull the stalk right at startup? If you wait even just a few seconds, you might not get into EV mode. What's your SOC at startup?

You'll get the single beep on a successful EV request if you're not on the Energy screen and/or if you invoke EV mode immediately on startup. If you're already on the Energy screen you won't get any indication other than the ICE shutting down.

You'll get the triple beep on a non-successful EV request if the ICE is already running for warmup, if you're travelling faster than 34 MPH, or if you're accelerating.

You'll also get the triple beep (and get taken out of EV mode) if you've invoked EV mode and then speed up to 34 MPH.

It is documented on the UK manual...
http://priuschat.com/index.php?showtopic=14582

Rejected when...
-The hybrid system gets cold. (After the vehicle has long been left below 0oC (32oF).)

Ken@Japan

European versions show a bright symbol on the dash when the EV switch is operated successfully so you always know when it's on. Not that it stays on for very long. If you start going up even a slight incline it will go off at once. I hardly ever use my EV switch and if there isn't one I would not recommend anyone to have one fitted unless you often need to move your car very short distances (less than 50 yards)

Where is the symbol located? (next to what other symbols)

My brother has the Coastal mod in his wife's 04 and he uses it quite often. Other than moving the car around the driveway, he often switches to EV mode as he is returning home. He told me that the ICE often just starts up for no apparent reason other than staying warm at the end of a drive and when you're returning home, you're going to shut it down soon anyway.

I often coax the car into stealth mode while I'm moving around my daughter's school or a large shopping center at relatively low speeds, too.

It seems to me that this kind of thing just screams for EV mode.

Thank goodness I have not read the UK manual ... it does work for me

Seriously though... maybe the key words are "has long been left." Perhaps the SOC gets down to 3 in that condition which is one of the more commonly known criterion for rejecting EV mode???

Actually I experienced the EV rejection right at startup at 32 deg F. This was after the car was allowed to sit overnight in the parking lot. Now during the rest of the day and evening there was no problem getting the EV single beep to occur during startup, because the engine hasn't had that long to cool down.

And yes I always pull the stalk right away at startup. I've gotten used to turning things on so fast that many times I lock or unlock the door just a fraction of a second sooner than the car is ready for me. I've also started the car a couple of times a fraction of a second before the SKS was sure my smart key was present and had to try a second time. So I did try and count a couple seconds after startup before pulling the stalk as well and was still met with the triple beep.

A couple days ago I was curious about switching on EV while stopped at a traffic light. Once again there was no audible that EV was accepted or rejected, you just had to trust on blind faith that it was accepted, and as I accelerated I confirmed it was. I accelerated nicely on electric until I met a hill and the car seemed to slow down rather quickly. I then pushed harder on the accelerator, and the car didn't respond and then suddely there was a triple beep, the gas engined roared too life and I accelerated very hard up the hill. So, yes, I can really see why Toyota would want to eliminate the EV switch in the US. This very abrupt and jerky behavior for real world driving would tend to cause poor gas mileage, could contribute to an accident, and would definitely draw terrible press from the US media.

So it probably does also make sense that Toyota applies appropriate constraints around the EV mode. For example if someone is driving a quarter mile from a parking lot to the unramp of an interstate highway in subzero temperature you do not want them driving in EV mode, Because if the gas engine were left stone cold while accelerating on the on ramp, I'd imagine the driver could experience some kind of stall as the gas engine struggled to come up in power from cold and the electric engine starts to cut off because the battery gets drained.

I did something similar to this one time and experienced a momentary "euphoria" of acclerating briskly up a hill getting 40 to 50 mpg! Both gas and electric were going hard, and my battery went from green bars to red bars in about 30 seconds! When I saw the frightening electric drain I lifted off the accelerator.

Yup. That's taken me quite a bit of getting used to myself. The big roar seems to be slightly delayed (in my experience) from the triple beeps. Try letting off just a bit, let the ICE kick in, and then accelerate as needed.

No.
We observed "the hybrid system" means the hybrid battery.
The CAN message of the hybrid battery temp becomes below 0C, we can't enter the EV mode.

Ken@Japan

Here's the dash from a right-hand drive 2005 UK Prius, showing the EV light on the right.
[attachmentid=2016]

Cool! Thanks! B)

My lights are arranged differently than yours, even if you reverse yours. Moving left from the speedometer there is the open door symbol, the word "brakes", and the seatbelt light. I suspect that, since your layout is that different, ours probably doesn't even have a spot for the EV light.

How did you get all the lights to light up together? I tried to do that, but I couldn't find a way.

Thanks again.

Got my EV mod kit from Coastal yesterday and installed it today. It's too bad Americans need to spend $55 and a few hours time to enable a feature that is already engineered into the car. Does anyone know Toyota's official reason for not enabling EV mode on the US verison? I've heard several reasons; 1) Possibility of EV mode shortening the battery life; 2) Potential lawsuits due to the car being too quiet for pedestrians to hear.

Also, has anyone compiled a list of ALL the differences between the US and European/Japanese versions of the Prius relative to appearance, emisions, features, etc?

Rick S

We have the international standard brake warning symbol, rather than the word "BRAKE". The US manual I downloaded shows seat belt, brake, door open, main beam, left turn - which seems to just be a mirror image to me. So I'm sure there's space for the EV light, but it's not actually there.

The other side's a bit different. We have sidelights, front fog, rear fog, left turn - you have right turn, blank, MAINT REQD, headlights.

Note the design of the dash is such that only lights on the top row will be on in normal operation, as lights on the next two rows reflect in the windscreen. Presumably the EV light must be far enough to one side where there's a wider shield.

Just switched everything on Main beam, dimmer to max, hazard lights, door open, EV mode on, front and rear fogs on.

That reference to topic 14582 doesn't show how the EV indicator
is connected to the ECU. That's what I'm looking for. Given that
the "hack" mod in the US involves adding a pin to the ECU connector,
I expect that bringing the indicator light out may involve similar
addition of connector pins, and that's what I'm looking for.
Please help the cause.
.
_H*

The Hybrid ECU talks to combination meter assembly via CAN bus.

Ken@Japan

So are you saying that the driver for the EV idiot light is in
the combination meter itself, rather than being connected directly
from some other ECU [as many of the other lights are]? Can the
appropriate excerpt from the EWD be placed somewhere for download?
.
_H*

Yes, that's right. There is no separate wired signal for the EV light going to the combination meter (as indeed is the case for many of the other lights). From this, we have to infer that it gets it from one of the ECU buses.