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EV mode disabled when too hot

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by driveprius, Jun 18, 2006.

  1. driveprius

    driveprius New Member

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    After experiencing the Euphoria of super high mileage during late Spring and early Summer (up to 57 mpg on highway!!), now I'm watching the mileage take a hit as the temperature hit's the upper 80 - 90 deg F. I guess using the A/C really does really take a toll even though it's drawing from the battery. Now sometimes my mileage dips below 50 mpg.

    One big annoyance is that with the hotter weather the EV mode seems to disable itself. Usually, first thing in the morning it's fine. But if the engine is allowed to get warmed up a lot, you start getting the triple-beeps that signal EV mode rejection. It also seems that once you enter this EV rejection zone it will last for about 24 hours. You can stop your car and let it rest a few hours and even in the evening with the temperature in the 80's it will still reject EV mode. Let your car sit overnight and EV mode will then work again.

    My guess is that once the hybrid engine gets beyond a certain temperature it triggers an EV disable mode that is timer set to last for many hours. The only question I have is why did Toyota do this? Did they think it was harmful to allow EV to work in hot weather?

    What I do know is that it probably contributes to my poorer gas mileage. Now I often have my battery fully charged at green and I can't take advantage of using EV mode to start my car from an initial stop. Plus sometimes when I'm in a parking lot with a fully charged battery, I watch as my Prius at times gets below 20 mpg instead of 99.9 mpg because it won't shut down the gas engine. I can't force the gas engine to stop because EV mode is disabled.

    It seems pretty clear that the sweet spot for the Toyota Prius is when the temperature is in the 70's F.
     
    #1 driveprius, Jun 18, 2006
  2. tomdeimos

    tomdeimos New Member

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    You need some instrumentation. Lacking that you just need to use AC more when hot, and if your car is parked in the sun, don't expect much from the battery during short trips. Figure on about 30 minutes in air conditioned comfort before the battery can cool enough to work much.

    On my last car I measured temps of over 140 deg in my car trunk, when the car was parked in the sun. This is way too hot for a battery.

    The battery cooling fan should run, but it won' do much unless your cabin is cool and it takes a while, just as it takes a while in winter to get warm enough.
     
    #2 tomdeimos, Jun 18, 2006
  3. driveprius

    driveprius New Member

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    <div class='quotetop'>QUOTE(tomdeimos @ Jun 18 2006, 12:30 PM) [snapback]273066[/snapback]</div>
    What you are describing still doesn't quite explain what I experience. I naturally run my AC when it's hot. However, when it's 95 deg F I tend to set the temperature to the mid 80's. If I set it to the 70's the Prius AC is just way to cold and I actually get a head freeze. But it's not like the Prius won't ever go into electric mode. It continues to go in pure electric mode, it's just that for those of us who have installed the manual override EV button, that manual EV mode seems to get disabled when the weather gets really hot. The normal automatically triggered EV mode of the Prius still continues to work in hot weather, only the manually forced EV mode seems to get disabled.

    If my battery is getting too hot, then I'd expect the Prius to shut down use of the electric motor completely. Also if I let my Prius cool off for about 4 hours in 78 deg F evening weather I'd kind of expect it to cool down sufficiently. I did this once and the Prius gave me triple beep rejections of all my attempts to activate EV mode manually.
     
    #3 driveprius, Jun 18, 2006
  4. efusco

    efusco Moderator Emeritus
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    The battery isn't getting "too hot" for normal hybrid operation but it's too hot to allow the EV override to function. Just like when the battery SOC gets too low to allow the EV override to function the ability of the car to run isn't disabled.

    The car goes to great lengths to protect itself. Use of the EV button could, if unchecked, allow you to drain the SOC to a dangerously low level or allow the battery to overheat to the point it could become damaged. When preset parameters are met EV mode won't work.

    The high ICE temp is NOT one of the factors that comes into play. The stage of warm-up of the hybrid system IS a factor as are Inverter temp, battery temp, battery SOC, and other hybrid system related factors that, unless you have the CAN-View or the Toyota THHT dongle you are not able to monitor and thus, can't exclude as the cause for the EV mode to enable.

    As someone who's been using the EV button for over 2 1/2 years and has teh CAN-View and was one of the first in the US to install this button I'm quite confident in saying that your theory about ICE temp being the cause of the EV mode failures is incorrect.
     
    #4 efusco, Jun 18, 2006
  5. hobbit

    hobbit Senior Member

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    As far as "lasting 24 hours" -- the battery is a fairly large thermal
    mass, and takes a while to eqalize to the cabin temp via the air
    duct. Meanwhile, any use of the battery tends to heat it more, so
    if it's already warm them obviously we wouldn't want it to get any
    warmer.
    .
    So skip EV mode and regulate your foot more carefully when it's hot.
    Your will probably improve anyways.
    .
    _H*
     
    #5 hobbit, Jun 18, 2006
  6. tomdeimos

    tomdeimos New Member

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    I think your questions have been well answered by Evan and Hobbit. And if you have a car that can handle can view, I recommend it highly. It takes a lot of the mystery out of these things.

    As mentioned already EV mode and normal battery operation are two different things. And if the battery ever shut down entirely due to being hot, we could not start our cars in the summer.

    But the EV mode allows a great deal more current flow when you accelerate and the actual battery current limits change with temperature and charge levels. So when the battery is hot the EV mode is the first to be disabled due to this higher current and therefore greater potential to make the battery even warmer.

    And though you can get regular battery mode operation when the battery is a bit hot, you will switch out of that also at a lower current than you can get when the temperature is ideal.

    This time of year I can generally go to work on my short commute, and beat 60 mpg. Coming home over the same route I rarely get over 55 mpg and often less. Less battery operation is a big part of this. The other big factor is traffic is usually worse.

    But if I go on a trip and drive with AC for over 30 minutes I can generally get full use of as much battery or ev mode as I want, even on 100 degree days.

    In winter I get the same effect but then it is from the battery being too cold. And in winter we have to also keep the engine warm.
     
    #6 tomdeimos, Jun 18, 2006
  7. ServoScanMan

    ServoScanMan Member

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    <div class='quotetop'>QUOTE(driveprius @ Jun 18 2006, 10:40 AM) [snapback]273039[/snapback]</div>
    I installed the 'factory' EV mode switch in my car. I noticed that when outside temp is above 90 degrees F, I can't go into EV mode. Maybe just a coincidence, but it's still anoying. Especially when the car sits for 1 1/2 hours in a parking lot and the battery is showing 6 bars. -
     
    #7 ServoScanMan, Jul 8, 2006
  8. K5VMI

    K5VMI New Member

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    It is amazing how timely may of these issues are. We have been experiencing 95 degree+ days on baton Rouge and I was trying to figure out the flakey operation of my EV Mode switch. Thanks for the explaination.
     
    #8 K5VMI, Jul 8, 2006
  9. ServoScanMan

    ServoScanMan Member

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    It would be nice is the MFD would display an error message or alarm when you tried to go into EV mode and the system would not let you. It would take alot less guessing on our part in trying to figure this out.
     
    #9 ServoScanMan, Jul 9, 2006
  10. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(ServoScanMan @ Jul 9 2006, 09:57 AM) [snapback]283327[/snapback]</div>
    I believe it does in the 2006MY. It does not in the '04/'05, but you get the triple beep so it's just as good as an error message IMO.
     
    #10 efusco, Jul 9, 2006
  11. powphilprius

    powphilprius Elshawno~

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    Cool, reading this thread has also answered my question on whether the battery is getting too hot. Has been 95+ this week and I'm getting the EV mode rejection. Worked this morning. Also, I noticed the battery fan is coming on, can here the air being sucked into the port by the back seat. So far I have not found the switch to be that useful. I can usually pulse drive enough to have ev mode happen anyway.
    Is everyone experiencing better mpg using the switch?
     
    #11 powphilprius, Jul 13, 2006
  12. ServoScanMan

    ServoScanMan Member

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    <div class='quotetop'>QUOTE(efusco @ Jul 9 2006, 02:13 PM) [snapback]283436[/snapback]</div>
    I do get a triple beep but that only lets me know that the system did not go into EV mode. I just would like a short message as to why it didn't go into EV mode displayed on the MFD. Yesterday, I was able to go into EV mode when the outside temp was 99 degrees. Maybe it's also has something to do with protecting the traction motor or inverter. I'm beginning to think if the electrical side of the drive train is to hot the system will run the ICE to help provide energy to move the car thus allowing the electrical side some time to cool down.
     
    #12 ServoScanMan, Jul 14, 2006
  13. ken1784

    ken1784 SuperMID designer

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    #13 ken1784, Jul 14, 2006
  14. randreed

    randreed Same as it ever was . . .

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    <div class='quotetop'>QUOTE(efusco @ Jun 18 2006, 07:49 PM) [snapback]273205[/snapback]</div>
    I just installed the Coastal EV mod (my second mod) during the 95degree heat today and I was frustrated by the 3 beeps and the message on the MDF, so I took a picture of the MDF with the message and came across this thread when I was looking for the best place to post my question. Of course this thread explained what was happening, and it makes perfect sense.

    Now that I've waited for the temp to drop I just went out and put the car in EV Mode with no problem at all. Thanks to the community for answering this in advance!
     
    #14 randreed, Jul 29, 2006
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