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Strange Driving Behavior with Battery Fan On

Discussion in 'Gen 2 Prius Technical Discussion' started by HighBreed, Mar 17, 2010.

  1. HighBreed

    HighBreed Member

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    2004 Prius
    It's a 2004 model with 106,000 miles, original 12V and traction batteries. Full tank of gas. It was 88 degrees yesterday, my A/C was running, set at 68 with fan on mid. I was driving on the freeway for 30 minutes when I noticed a substantial loss of power. I have to press the gas pedal harder to maintain 55 mph.

    The freeway was flat so it's not like climbing uphill. I have to press the gas pedal more than usual and I can hear the engine laboring.

    I looked at the MFD and saw I was on the two pink bars. Unusual because I've been driving for quite sometime, 20 - 50 mph rush hour freeway traffic.

    I also noticed that the battery cooling fan was on. This is the first it happened.

    When I got home, I let it rest for 20 minutes and hoping that hhmmm, maybe, it needs to reset itself. So I drove on the surface street and the same problem reappeared.

    The transition from EV to ICE or any combination thereof comes with a very noticeable, almost violent, jerking motion, like power-shifting a manual transmission. And in order to accelerate normally, I have to push my gas pedal deeper. I have to press it hard or I will not move. Where the ICE would come on before as almost imperceptible, this time you can really feel it and hear the engine laboring. The synergy drive display shows constant changing of ICE/EV combination.

    Leaving a stop light, it almost feel like the car would hesitate first and then suddenly it would go. But it won't go fast. I have to keep the pedal depressed harder than normal to maintain street speed of 40 mph. And because I have to step on the gas more, my average MPG dropped to 37 mpg. I usually average 46 - 48 mpg in winter.

    The battery fan also came on after a few minutes of driving and stayed on. I was showing 4 or 5 blue bars on my MFD. Whether the A/C is on or off, the problem persists.

    There's no check engine light. What do you think might be the problem?
     
    #1 HighBreed, Mar 17, 2010
  2. linuxpenguin

    linuxpenguin Active Member

    Joined:
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    2005 Prius
    Have you verified the integrity of the 12v battery? If it's still the original battery I'd say that's a good place to start, they typically don't last that long...and all number of crazy / bizarre things can happen when it starts to die. It's not incredibly likely to be the cause, but it's worth investigating.

    The sluggish acceleration comes from the vehicle limiting the amount of electric energy it draws from the battery to drive the car (when you accelerate from a stop, the car first uses the electric motors and then the gasoline engine comes on to assist which is why you're seeing sluggish behavior). This could indicate a dying traction battery, but I would start with checking the 12v first. The Prius traction batteries should last longer than 100,000 miles...

    If it is the traction battery that is dying there are places that will sell you used traction batteries for far less than the dealers sell new ones.

    EDIT:
    One other thing I just thought of after re-reading your post: If the batteries are getting very hot then that would cause the situation you described without there actually being a problem. When the batteries get hot the vehicle limits the power it draws from them to prevent damaging them (and the batteries heat up after long drives and can stay hot for awhile since they have a high thermal mass). Is the fan turning on quite loudly or is it very hard to hear? In the Gen2 the fan doesn't turn on until they get to 94F and gradually gets louder as the batteries get warmer...Is the battery fan intake obstructed? It's in the rear right side passenger area by the door.

    Andrew
     
    #2 linuxpenguin, Mar 17, 2010
  3. Prius 07

    Prius 07 Member

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    Make sure the vents for the HIV battery pack are not blocked.
     
    #3 Prius 07, Mar 20, 2010
  4. uart

    uart Senior Member

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    Hi highbreed. It does sound like your HV battery might be failing. Excessive heating of the battery is a definite sign of impending failure. Please note however that it might still be something considerably less drastic, like a sensor failure or something. Anyway, if you're still under HV battery warrantee then you should get it checked out by the dealer ASAP.
     
    #4 uart, Mar 21, 2010
  5. richard schumacher

    richard schumacher shortbus driver

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    #5 richard schumacher, Mar 21, 2010
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