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2011 Prius battery load test using halogen head light

Discussion in 'Gen 3 Prius Technical Discussion' started by fortec, Jul 20, 2022.

  1. fortec

    fortec Junior Member

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    I was having a P0A80 moment in my 2011 Prius for about a month now. I managed to get the car to move along by clearing the codes. But it eventually comes back. My "freeze frame data" show blocks #6 & #11 as being about 2V lowers than the highest block. That would be of concern, right?

    So I went and tried the load test to pinpoint the exact cells that are causing the code knowing that blocks #6 & #11 are most likely to be the culprits. I connect a multimeter across each cell and start with the #1 cell being right next to the ECU. At the same time, I also put a Sylvania 9004/HB1 at a high beam across each cell for 2 minutes.

    The results show my cells run from 8.0v to 8.3v without load. With load after 2 minutes, the cells return from 7.4v to 7.9v. With the 7.4v, the was a 5 minutes load test. Overall, I am surprised by the result. I was expecting a few cells would drop really low. But the data shows otherwise.

    Did I do my load test right? It seems my cells doing well.

    I also took out all the busbars to soak them, and scrub them to remove all the buildup. Before putting the busbars back on, I coat each one with dielectric grease. My 1st test drive so far seems normal. But the 2nd test drive shows a sudden drop from 7 bars to 3 bars which concerns me. I am going to drive it until it gives me another code. Then I will read the "freeze frame data" again. I know the problem is still there.

    I am tempted to purchase 4 cells to replace blocks #6 & #11 and then move the good cells in the middle toward the ends. What do you think happened?
     
    #1 fortec, Jul 20, 2022
  2. JC91006

    JC91006 Senior Member

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    you don't really have to load test the modules on block 6 and 11. They both should have at least 1 module reading in the 6v range. That's why you have the code triggered
     
    #2 JC91006, Jul 20, 2022
  3. fortec

    fortec Junior Member

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    I thought of the same too and was expecting to see what you are saying. But why it is not so when I load test them individually? To me it's puzzling! In fact, none of the 28 cells goes below 7.5v after the load test.
     
    #3 fortec, Jul 20, 2022
    Last edited: Jul 20, 2022
  4. JC91006

    JC91006 Senior Member

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    To get an accurate reading, you have to let the battery pack sit for a week. After the week, all the bad modules will show.

    It seems like you tested all the module the same day you drove the car, that's why the readings are so high. You have to let them sit and settle before doing the readings/tests.

    Also next time you don't have to use dielectric grease. That stuff just makes your job much harder next time around. It is not needed and is very hard to handle when you need to do the work again.
     
    #4 JC91006, Jul 20, 2022
  5. fortec

    fortec Junior Member

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    Actually, I did the test the day after. But I think you're right. Maybe I didn't let it sit. I think I will go ahead and change out the 4 cells from blocks #6 & #11 then I will let those sit just to prove to myself that I do indeed have bad cells. Thanks JC...
     
    #5 fortec, Jul 20, 2022
  6. JC91006

    JC91006 Senior Member

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    If you're going to be doing a proper load test on all the modules, you might be able to find more weak modules.

    I normally have to charge up all the modules before doing the load test, so they are all discharging from a full charge. After 2 minutes, the ones that drop a significant amount would be the ones you need to switch out (or try reconditioning). This is a very time consuming process for 28 modules.
     
    #6 JC91006, Jul 20, 2022
  7. PriusCamper

    PriusCamper Senior Member

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    You're supposed to record the voltage reading at exactly 2 minutes, before you disconnect the light bulb... Also you need to only replace bad modules, not whole blocks. The goal is for all 28 modules to behave the same way and be of similar age and number of times it's been discharged. When you double up on modules that might not match in the same block, you double up on odds of warning lights coming back because the new modules don't match.
     
    #7 PriusCamper, Jul 20, 2022
  8. fortec

    fortec Junior Member

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    Let me understand this right. You charged up all your modules, all 28, before doing the load test? That would defeat the purpose of letting them sit for a week, don't you think? Or are you charging them up and then letting them sit for a week before doing the load tests?
     
    #8 fortec, Jul 20, 2022
  9. JC91006

    JC91006 Senior Member

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    I like charging them so I know they are all full before I discharge. Letting them sit for a week will let you know which modules can hold a charge and which modules can't. The ones that can't and are bad will be much lower in voltage than the rest of the pack.
     
    #9 JC91006, Jul 20, 2022
  10. JC91006

    JC91006 Senior Member

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    When you did your discharge, you recorded the beginning voltage and ending voltage after 2 minutes correct? The ones from block 6 and 11 should be way off.
     
    #10 JC91006, Jul 20, 2022
  11. PriusCamper

    PriusCamper Senior Member

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    For me the answer is both... Load test data from a fully charged pack that's been sitting for a few days gives a different perspective on module health compared to load test data from a bad pack as soon as I put it on the work bench. Without tens of thousands of dollars of lab grade testing gear, these testing differences can be helpful.
     
    #11 PriusCamper, Jul 20, 2022
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