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Is my traction battery going bad?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jdonalds, Jun 28, 2015.

  1. jdonalds

    jdonalds Active Member

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    Has anyone else experienced anything like this before? A 10-12 mpg drop over 500 miles or more, then returning to normal?
     
  2. uart

    uart Senior Member

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    People sometimes experience temporary changes in the reported MPG after the 12V battery has been disconnected and the ECUs reset. Has anything like that happened recently?
     
  3. jdonalds

    jdonalds Active Member

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    I replaced the 12V battery in 2014 after which there was no change in mpg.

    The next time I disconnected the 12V was after the low mpg problem came up. I cleaned the HV fan and dropped a plastic clip behind the 12V and had to take that battery out to retrieve the plastic clip.

    So in this case it was not related to disconnecting the 12V battery.
     
  4. gdanner

    gdanner Member

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    If you are comfortable working inside the HV battery (or you know someone who can safely do this), Then I'd suggest a physical inspection of the interior of your HV battery:
    • Check for looseness and/or corrosion on the 56 8mm hex nuts and copper tabs that make electrical connections to the studs on the 28 individual modules.
    • Also check all electrical connections that go through the battery ECU compartment.
    • Look for any signs of individual battery modules leaking fluid, overheating, or swelling up
    • Check the 4 thermistors (3 underneath, 1 on top) that measure internal battery temperature (and be careful not to break them when inspecting)
    • Look very carefully at the thin wires that go into the orange connector on the battery ECU. These wires are how the ECU detects battery condition. If even one is open or intermittent there will be problems. Only a few mA of current flows through these wires, but they are very important. Make sure there is NO corrosion or dirt on this orange connector or on the socket it plugs into inside the battery ECU.

    One good thing is that your car (hopefully) hasn't produced any DTC codes yet. In my case I observed a gradual drop in mpg for the past 6 months. Then my car abruptly started to throw frequent POA80 codes. Although I rarely watched the Prius bar graph SOC display in the MFD prior to when my car started to throw codes, I do think the SOC was varying more than it used to. With 2 modules replaced my SOC now stays between 55 and 70% no matter what I'm doing with my driving. When I had a bad module in my battery the SOC would often jump from top to bottom in minutes, even when there wasn't any DTC code.

    So if your SOC was all over the place (along with bad mpg) and then it magically got better all by itself, that's why I'm thinking maybe there are some loose connections or corrosion inside your HV battery.

    Best of luck with fixing this!
    -EB
     
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  5. jdonalds

    jdonalds Active Member

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    EB, That all makes sense. Loose or corroded connections could be at fault here given the range of issues we've experienced. Too bad our cable and software didn't show up when the car was misbehaving.

    One factor that could come into play, and aggravate loose or corroded connections, is the weather. Of course being in California we haven't had any significant rain since April (less than 1/2 inch in May, June, July). However the temperature cycles come close to matching the car's behavior.

    We had over 105 degree high temps for about three weeks in a row. Then a few days ago the high temps dropped into the high 80's to low 90's. It's supposed to warm up again to the mid 100's starting this week. Heat of that kind is rather normal for Redding CA in the summer. I'm not suggesting the heat itself is an issue as this is our 5th summer here. Rather what you wrote + heat could be a potential cause.

    At this point I'll wait for the hot weather to see if the poor mpg conditions return. If they do I'll tear the car apart once again and check over the connections.

    Thanks for your help.

    I drove the car this afternoon and everything seemed normal. The avg mpg on the car's display is creeping back up and is almost to 43 mpg on this third tank of gas since the problem started. The first 1/2 of this tank were in the mid 30's.

    I do watch the Prius bar graph SOC and did notice the poor behavior. I've always respected the Prius design engineers for the Synergy drive and Atkinson engine out of which they squeezed such great mileage. I doubt if I have ever ignored the SOC or 5 minute bar graph for a full tank of gas. I don't do extreme hyper-mile'ing but I'm willing to drive 39mph in a 45 mph zone as long as no cars are behind me. My wife thinks I'm crazy. A also do pulse and glide sometimes but never when my wife is with me. So I'm pretty informed as far as this car's behavior.

    I have to say again that the Prius is pretty hard to beat from my perspective. The 20 Cu Ft of cargo space simply isn't available in any sedan, and 45+ mpg isn't available in any other car with that much cargo (small SUV). We like the ride, the features, the comfort, the rear seat leg room, smart key system, and of course the $7,000 in gas savings we've had over the years. I would be thrilled if this mpg problem turns out to be nothing more than connection issues.
     
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  6. RogerHq

    RogerHq Junior Member

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    If U want to take control over your HV battery pack, use the data coming from Prius own monitoring sensors. I believe U all have them there, 14 cellblocks consisting of Panasonic NIMh cells constantly monitored wirelessly by iPhone or AndroidApps. The keyparameter is I believe, the 2195 PID who measures internal resistance in every single cell block. If that starts to rise, then you know U have a problem. In my replaced pack the value stays at 0.02-0.03 Ohms. That will deliver some heat into the battery if U take out 100Ampere during acceleration or push it back during regeneration. Heat is also measured as mentioned above, the three thermistors are probably TB1 to TB3 associated to PID2187. During driving I notice a temperature rise from ambient to 10 Celcius above, for now 30-38 deg C dependent on driving style.
    (My data is taken from EngineLink, iPad-version with the Toyota PIDs selected)
     
    #106 RogerHq, Jul 15, 2015
    Last edited: Jul 16, 2015
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  7. RogerHq

    RogerHq Junior Member

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    What about repacing the cells in my old HV battery pack, is it any profit in that?
     
  8. jdonalds

    jdonalds Active Member

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    Sounds interesting. Do you know of the name of the app for Android? Is there any other hardware required for this wireless connection?

    We continue to have problems but they are intermittent. We still can't get a tank of gas over 40 mpg but often the car is behaving normally. Then for several hours it again faults and we are averaging in the low 30 mpg range. The best we've had for a full tank recently is about 40.5 mpg. I just haven't bothered to hook up the laptop and run the software again. I'd have to catch it when it is failing.

    If the app you speak of can be used at anytime without the laptop it would be so much more convenient.
     
  9. jdonalds

    jdonalds Active Member

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    Never mind. I found "Torque" and will likely buy the bluetooth adapter. I wish I would have known about this first before burning up so much time and energy on TechStream. This seems like a much better tool.
     
  10. gdanner

    gdanner Member

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    I've been using Torque on my LG G3 Android smartphone for 3 weeks. I purchased this OBD2/Bluetooth adaptor at Amazon:


    So far this adaptor has worked perfectly in my 2005 Prius.

    I created 3 customized dashboard displays that I use while driving. I've also been logging data and analyzing it later.

    There are several "name brand" ODB2/Bluetooth adaptors that cost more than the $ 23.99 I paid for this "generic" unit, but I don't know if those more expensive units work any better?

    -EB
     
  11. jdonalds

    jdonalds Active Member

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    Thanks. That's the same bluetooth adapter I ordered. I'm anxious to receive it and put it to use. Perhaps I'll get somewhere with this new option.
     
  12. jdonalds

    jdonalds Active Member

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    I now have the Bluetooth adapter and have been setting up Torque. I'm quite pleased with this setup, I've even ordered a cheap 9" tablet so I can take advantage of the larger display and have more data on the screen. My Galaxy S3 already limits me.

    At the moment the Prius is behaving near normal so there isn't much to discover.

    It really irritates me that I paid Toyota about $75 to check out the HV battery. All they did was test drive the car for 7 miles, and check for codes. Now that I see the huge amount of data available using Torque paying Toyota was a total waste of money.
     
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  13. SageBrush

    SageBrush Senior Member

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    My local dealer wanted $125 to read engine codes. Lucky for me, I woke up first and drove across the street to an auto store that read the code for free. The gas cap was loose ;)
     
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  14. jdonalds

    jdonalds Active Member

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    I had the same thing happen to my 4Runner. The gas cap was broken. I had the SCAN II hooked up in the 4Runner which did a nice job of telling me what was wrong.
     
  15. jdonalds

    jdonalds Active Member

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    I thought I'd through in an update. I've monitored the HV battery using the Bluetooth ODB2 adapter and Torque Pro app. I haven't seen anything wrong with the battery, it seems to be working as perfect as I could expect. So I have no idea what is behind the lower mpg.

    We are getting normal mpg on 100+ mile freeway trips locked on cruise control going 65-70mph. We get about 48-50 mpg. So I don't think we have a rolling resistance issue like dragging brakes.

    Our problems are all around town, typical stops for stop signs and red lights. These are trips that we know well and haven't changed our pattern. Where we used to get 45-47 mpg we are now getting 40-43 mpg. Over the span of about five or six tanks of gas the initial 35 mpg issue has slowly improved to the 40-43 mpg we've seen lately. I have no explanation for this.

    To make things more complicated we had to put new tires on the car. They are Michelin Defender ST type which I understand will likely drop our fuel economy by 2-3 mpg. So we'll be watching for 37-40 mpg around town now.

    Bottom line. I don't know what is wrong with the car.

    I've monitored HV Internal Resistance and HV Battery Block Voltage for all 14 cells.

    The only interesting thing is the last two tanks of gas have shown about 4-5 mpg less on the Gen II display than calculations at the pump. Two tanks isn't enough to set a pattern though. Over the years I stopped checking using a calculator at the pump because the result was always within +/-2mpg from the car's display. So being off by 4-5 mpg is far from our historical data. I wonder if there is something in the flow meter that could go wrong and make us think we are getting less mileage than we really are.
     
  16. Mendel Leisk

    Mendel Leisk Senior Member

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    To definitely check for dragging brakes, get into a habit of feeling the wheels right after driving. If they're all about the same, and barely warm at most, your brakes aren't dragging.

    The Michelin Defender's likely are bringing your mpg down; that's at least part of it. Michelin on their website acknowledges them to to be 2 steps down (on a scale of 10) for "fuel economy" (Energy Saver A/S are highest rated at 10, the Defenders are 8).

    I would just do your calculations based on fuel pumped in and distance travelled, eliminating any vagaries of the Toyota display.
     
  17. kinglew

    kinglew Member

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    Just bought a set of defender for our 2 Prius seems to a great tire as good as the harmony on my Prius .how do you like your set?
     
  18. jdonalds

    jdonalds Active Member

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    There is no question the Defenders are smoother riding, quieter, and better handling than the Michelin Energy Savers we replaced. I would have gone with the Energy Savers again but we were up against a wall. I had a nail in one tire that was not repairable. Long story short we couldn't wait 3-4 days so I went with the Defenders.

    My intention is to buy a Gen IV as soon as they are available so the loss in mpg with the Defenders won't mean much of a $ hit. Having relatively new tires will help when we sell the Prius.
     
  19. jdonalds

    jdonalds Active Member

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    I have one of these: [​IMG]
    Pretty cool, and inexpensive, digital instant temperature gauge.


    In an attempt to determine if any of the brakes on my Gen II were dragging I've kept the digital tool in the car. After a couple of drives I quickly exited the car and checked the temperature of the brake discs. All were cool and with in the range of 120 - 140 degrees F. So no dragging brakes.

    I do have a dragging brake on my boat trailer. I checked it a few days ago and it read 330 degrees. The wheel was sizzling. I have to replace the brakes on that wheel.

    I still have no clue why the mileage on our Prius dropped. Highway miles are fine. It's just the around town slower speeds where we are taking the hit. Many other car owners would be thrilled to be hitting 42-43 mpg. We Prius owners know better.
     
  20. RogerHq

    RogerHq Junior Member

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    Have been occupied for a while, nice to see other working for the cause ;-)
    Obviously the issue of less gas mileage is unsolved for you, jdonals.
    U haven't mentioned any analysis of your combustion engine?
    There is some parameters to check in my app eg. engine temp, oil pressure, rpms, ignition angles etc, etc...with the Volkswagen debacle in full swing the most obvious reason for less mileage is changed or unstable combustion engine parameters. Is such an analysis already done jdonald?