Power loss & low battery during climb

Discussion in 'Gen 2 Prius Main Forum' started by Tone88, Jul 2, 2011.

  1. J Moberly

    J Moberly New Member

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    I have this same issue, just bought the car with 100k miles. No clearcut solution eh? I took it into the dealer, the techs at Toyota came back and said there is no problem with the car, no codes were thrown and the battery tests good, I'm going to send it back to them to have them retry. I can't go above 50mph uphill, it looks like it happens when the battery shows depleted, as it pulls fine until I've been driving uphill for a few minutes. The car just seems to lose 80% of it's power. This is my first Prius and this is very unnerving :(
     
  2. nh7o

    nh7o Off grid since 1980

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    It has been noted many times here on PC that Toyota techs usually work from set diagnostics, and they do not all have the same experience with the Prius, by a long crack. So they can be mystified pretty easily. The bottom line with Toyota is that unless the car sets DTC's, there is no problem.

    Assuming the car's MPG is OK (something better than 45mpg hopefully), low power when climbing hills or accelerating can be due to several things, including:

    * Overheating of inverter/transaxle. Check for coolant flow by looking in the inverter reservoir with the car Ready. Make sure the 12V battery is good, as a failed 12V can cause the 12V charger portion of the inverter to overheat.

    *Overheating of the HV battery. Check the battery cooling fan (instructions posted here) for obstruction. You should be able to feel air flow, and hear it running, by putting your ear next to the inlet in the back seat passenger side.

    *Poor engine power, causing the car to rely on the HV battery excessively. Could be spark plugs, dirty intake filter, dirty MAF, poor gas flow,...?.

    *If the HV battery has low capacity (display shows frequent variations from green to purple bars), the engine will end up spending too much energy recharging it, and that will rob the overall power available to climb the hill. A bad HV battery will overheat, and that results in the cooling fan running audibly rather than its usual quiet purr.

    If the overall MPG is not OK, then there are other possibilities, like low tire pressure, poor alignment, brake drag.

    All these aspects have to get *really* bad before they will set DTC's, even though driveability issues are apparent.

    I go up major hills here, and I note that the battery is *not* used while going at a reasonable, steady speed. It only gives up discharge current flow when accelerating, or briefly going up more steep sections. But it never goes all the way down into purple bars. The car should have enough power to run at steady state on engine power alone. The hybrid system is only there to capture and release the transient energies of short term change, not to provide long term power.

    But the car is definitely *not* a mountain goat, and it will not keep up with the many cars going up hill at 10 or more mph over the speed limit. They are getting maybe 10mpg or less under that condition. Some places I am fine with going 50mph, and not trying to keep up with the monster 4wd trucks going 75mph. I don't know how these guys can afford the gas.
     
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  3. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    All agreed except this portion.

    We have the Rocky Mountains here and the Prius is a well capable mountain goat. It maintains 80mph or higher going up I-70 which contains the steepest sections anywhere in the interstate highway system through ski country. The battery will deplete fully to 1-2 bars on the way up and completely replenish to 8bars on the way down. Both are suboptimal conditions that the car automatically deals with.

    And as stated, the car has plenty of umph to maintain a speed. It does not have enough power to speed up on the grade with the pack depleted. If you are a micromanager driver constantly applying gas and brake and adjusting the wheel (many people are and don't even realize it) you are going to lose speed because everytime you twitch at the pedal, you slow down.

    The Prius gets roughly 8mpg to 16mpg going up the mountains near my house, every day, at least 2 times a day. By comparison the RX450h gets 4-10mpg (half as much essentially). It is just something you have to take to live up a mountain.
     
  4. nh7o

    nh7o Off grid since 1980

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    OK Toaster, all noted. I don't think mine can manage 80mph going up a decent hill with 2 people and some stuff. Maybe the difference is cool dry air there as opposed to the wet hot air here.
     
  5. uart

    uart Senior Member

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    Seriously, if was losing 80% (or 80+ percent as per your other thread) of it's power then it wouldn't be maintaining 50 MPH up hill, it would be more like 15 MPH.

    Wildly exaggerating things is not going to help anyone diagnose the problem, neither here nor at the dealers.
     
  6. seilerts

    seilerts Battery Curmudgeon

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    Once SOC falls below 40%, the car becomes a turtle. Get a Scangauge or PriiDash and monitor SOC and battery current when you are climbing the grade. You may find SOC in the 30s and a positive battery current. Basically the car is trying to charge the battery while at the same time climb the grade and there is a significant drivability problem. It happens on batteries that are weak, for some reason SOC overshoots the 40% lower bound of battery control.
     
  7. THF

    THF Junior Member

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    I've had this problem whenever we went up a mountain. I'm glad to know that there is nothing to be real concerned about.
     
  8. tonyBBQ

    tonyBBQ Junior Member

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    interesting to find this thread. I just drove from Oregon to New York last week and I experienced this loss of power. I am very observant when it comes to elevation changes and, in fact, hardly use cruise control because it wont actually give you the best MPG. It's all about slow acceleration in anticipation of a large hill and using less power on the descent. This aside, there was a time when a hill on I-80 lasted over a mile so I started around 80 MPH and eventually dropped to about 45 MPH after a while. the battery was in the red and I figured i should slowly speed up to at least 55 to not inconvenience the semi drivers. When trying to accelerate I could here the engine increase in RPMs but it wouldn't increase my speed at all nor would it deliver any power to the battery pack. i pushed the pedal down pretty far, but didnt floor it because im not an idiot. It seemed like a lost cause and worried me a bit. It was very odd. this lasted for a few more minutes until the hill finally flattened out. I drive a 2007 Prius with 170k on it. nice to find this thread and know Im not the only one!
     
  9. patcoghm

    patcoghm Junior Member

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    No power on hills, MPG down, SOC low, PROBLEM FIXED
    No power on hills, MPG down, SOC low, PROBLEM FIXED | PriusChat

    tonyBBQ. You have all the problems that I just solved. Its the VVT system and the Oil Control Valve that advances and retarders the timing which gives the power that your missing. Read the above post and its the same problems. Just replace this valve. On my second tank and my mileage jumped, power returned, and I can accelerate on hills. Its not the nature of the car as some have said to bog down on hills. Do not test this valve as mine tested OK, but I think it fails at high speed due to excessive heat and the coil that actuates the valve fails. Works in town for acceleration so its a false positive. Just had this happen on my last trip over a pass from Eugene Oregon, lost power, but for a few seconds it actually kicked in and I accelerated. That was my clue it was a intermittent problem. Had these problems only on high speed at level driving or hills. So it doesn't really appear as a normal problem. You might get a P0011 code which disappears after back to city driving. My guess is this valve is defective and I'm seeing its been out for 5 years and maybe never worked except the first few years, ans its normally used it accelerate, for high speed, and hills controlled by the gas pedal.
     
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