For Traction Batt Fail - limp mode idea?

Discussion in 'Gen 3 Prius Main Forum' started by Slider2732, Aug 14, 2019.

  1. Slider2732

    Slider2732 Junior Member

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    Recently, we had a drive around town, paying bills etc. All was a case of either driving through a paying center or dropping things off. 15 miles total, something like that.
    Got home and switched the car off - 21.7MPG :eek:
    It was a stonkingly hot day, 100F and we don't normally do such slower town driving at 2 p.m in the blazing sun. Before and after, the same sort of run has resulted in ~50MPG. Every time we make such a run the car returns high 40's or better, at least on the MFD.
    The car is driveway based, but well shaded. 90K miles, EGR pipe cleaned, rear seat fan cleaned, no issues in a year of ownership. Original 12V, with regular solar charging (will be replaced at service).


    Well, I read (somewhere) the car shuts down the traction battery completely when it detects an overheat condition.
    First of all, is the info correct?
    If true.... there should be a fix for stranded motorists where battery errors pop up.
    Could a fella put a wire across 2 sensor pins and cause the condition when the traction battery is locked out?
    The car won't drive with a failure error. Causing the false positive heat condition would at least allow a stranded motorist to get home.
     
  2. jerrymildred

    jerrymildred Senior Member

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    I don't have a definitive answer for you, but maybe I can fill some gaps.

    I think it will put a stop to the hybrid system if either the battery or the inverter gets too hot. Same with the transaxle. If it was the battery getting too hot, I'd think you would have heard the cooling fan trying to cool it off. The battery would get hot if the cabin was hot or if the cooling fan wasn't moving enough air.

    I'm more inclined to guess that it was the inverter or transaxle that got hot because of the high temperatures and low speeds involved.

    Shorting (or cutting) the sensor wires would only make the computer think that the temperature had gone to infinity at one end or the other. Even if you could make that work, you'd stand a good chance of causing some serious and expensive damage by bypassing a system meant to protect some very expensive components.
     
  3. WolfpackBill

    WolfpackBill Active Member

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    Were you running the AC for your errands? The AC does use a lot of energy to keep the car cool. So when the AC is running the battery down to the point where the engine kicks in to recharge the traction battery, you use gasoline, hence your low MPG. That is something I experience a lot when I get out of work in the afternoon when temperature is usually in the 90's and with high humidity and with a few long red lights getting away from work.
     
  4. bisco

    bisco cookie crumbler

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    if the engine starts, the battery is working. it may be limiting charge and discharge rates though.

    hard to gauge all your parameters, but its probably fine.
     
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  5. Grit

    Grit Senior Member

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    It's summertime so we're getting a bulk handful of similar threads; hv bat overheats and ICE only propels. Pull over and put on Park, keep AC on, HV intake fan will suck in cool air into the pack. Once it's cool enough, you can drive with both hv bat and ICE together and not be a traffic hazard.
     
  6. Grit

    Grit Senior Member

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    It was 104F on way back home today and still yield great MPGs with AC on w/intake mod

    2BDC11E5-DCCB-4B55-B8BA-89EEFFC569E1.jpeg
     
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  7. lech auto air conditionin

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    There’s one thing most people don’t know and don’t think of if you’re just a few ounces low on refrigerant the air conditioning programming does not know this when it looks at the sensor to see if the cabin has been cool enough based upon your temperature selected but because there’s not enough refrigerant we cannot meet these parameters so it tells the compressor to wind up its RPMs to work A little harder which uses more power and after a period of time if it still does not see that temperature has been satisfied it will wind up the compressor even more this is a never ending loop of self-destruction and low gas mileage . That was 33 miles to the gallon on my trip below with the air conditioning at the lowest setting with the fan speed at the highest setting over 800 pounds of tools and equipment inside the car over 500 pounds of tools and equipment towing a trailer with a oversized extra large roof rack on top. I have a little bit of experience with Prius air-conditioning and if I could tell you one thing for sure a few ounces of refrigerant make a difference in your gas mileage. And the longevity of your electric compressor it also causes your HV battery to cycle more often which also shortens the life of your HV battery over the long run .
     

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  8. Slider2732

    Slider2732 Junior Member

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    Many thanks for the great replies :)
    It seems the opinion from you fine fellows is that while rigging the overheat sensors might work, it could cost more than a tow truck haul for anyone stranded. I agree, on thinking about it. Any service center would look at the mod/tape/dangly safety pins and start huffing and blowing.
    Well, it was just an idea, that launched into the conscious.
    Thanks also for asking about the event itself... never harms to add to the database of knowledge.

    Jerry - would changing the transaxle fluid make a change?
    Am just wondering if old fluid has worse heat dissipation than new. Cloggy, to use a word.

    Yep, the A/C was on. I did though make sure the traction batt wasn't low. It was at 2 bars from full. It is however unknown if the level changed, it would have solved whether the traction batt was locked out (my own Hindsight sensor wasn't plugged in).
    We've used A/C maybe 4 times in the year of motoring. In fact, I cover the car to limit UV every day - no black tint on the windows, plus we got really bad clearcoat peeling on our previous car, 2001 Ford Escort. That's also why we drive about at vampire hours, anything over a few years old seems to get huge swathes of missing clearcoat in Oklahoma. See the gap between the car and the white wall of the shed in my pic? that's where the car port is going soon.
    All I did was press the A/C button, with scant regard to what temperature was set. It would have to be cooler than "OMG my skin will peel off in this heat!"

    The low refrigerant is an excellent point. We wouldn't know if it was any different to 'usual'. Will check that.

    Some running around was done this morning, wife driving, the car returned high 40's MPG.
     
  9. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    That sounds plausible, but is it robbing Peter to pay Paul? I guess I'm at loggerheads with the lot of AC-to-cool-the-battery proponents here. My take, AC is a net minus in that endeavour.
     
  10. Grit

    Grit Senior Member

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    With my mod, no winds for the last 7 work day commutes and same cruise control set points, I’m typically down 1 to 2 mpg loss overall with AC while hv bat remains in the low 80Fs range. 64mpgs with AC, 65 to 66 mpgs w/o AC. So Not that big of a loss of mpgs instead of letting hv bat go up to 100F +
     
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  11. jerrymildred

    jerrymildred Senior Member

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    I won't hurt to change it, but if it won't help. If it was clogging, you'd be having huge problems.
     
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  12. jerrymildred

    jerrymildred Senior Member

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    I use it to cool me. The battery gets cooled as a bonus. But w/o the A/C, I'd smell REALLY bad in short order. And so would the car. I'd also be minus a wife because there's no way she'd tolerate sweating like a horse for no good reason.
     
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