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High delta SOC and other symptoms

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Nat C, Jul 10, 2014.

  1. Nat C

    Nat C Junior Member

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    Apologies for the cross-posting, this is following from my comments on someone else's thread but that conversation seems to have stalled. I'm hoping someone can share some diagnosis suggestions for my '05 Prius (101K mi) that has been exhibiting abnormal HV battery behavior.
    • With city driving, the HV battery is consistently being run down to one purple bar on the SOC meter. Have been experiencing this for at least the last week+.
    • When this happens, acceleration becomes very sluggish and the ICE runs almost constantly as it tries to charge the HV battery.
    • I checked voltages with a mini VCI/Techstream, but there don't appear to be any outlier blocks.
    • The max/min voltage seem to track okay (within 0.1–0.3V).
    • Delta SOC% is very high—consistently running at ~80%.
    • HV battery SOC appears to drop at 0.5% every 1-3 seconds even with the car stopped and/or in P.
    • No error codes are being generated (yet).
    I saw on the Gen II troubleshooting sticky thread that ECU or the invertor might be culprits. Can I check these with the mini VCI? Are there other possible maintenance issues that I should consider? What might the high delta SOC indicate?
     
    #1 Nat C, Jul 10, 2014
    Last edited: Jul 10, 2014
  2. nh7o

    nh7o Off grid since 1980

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    The usual symptoms of poor battery is for the SOC on the display to fluctuate from low purple to green and back. Yours seems to just go down and stay there, if I read it correctly. It would be good to know what the definition of the delta SOC parameter was, somewhere in the software it should have a definition.

    Some questions: What happens if you force charge the HV battery, by shifting to D, keeping foot on brake, and pressing accelerator pedal until the engine comes on? You should see the battery climb to blue and green eventually. Use the techstream to look at the amps coming from MG1 and MG2, and going to the HV battery.

    What is the instantaneous MPG readout if you travel at a constant speed of ~50mh on a flat road, no wind? (assuming the car will do that.)

    The idea is to determine if this is a problem with poor charge current produced, or perhaps inverter limitations due to cooling problems. It is difficult that the car is not producing DTC's, which again shows how badly the driveability can degrade before error conditions are met.
     
  3. Nat C

    Nat C Junior Member

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    Thanks for your help yet again!
    1. Yours seems to just go down and stay there: There have been some instances of fluctuation, but yes, mostly it just drops low and stays there.
    2. definition of the delta SOC parameter: "The normal, low to high SOC deviation is 20%. If the Delta SOC exceeds 20%, this means that the HV battery ECU cannot correct or maintain the SOC difference within the acceptable range." (source)
    3. what happens on force charge?: I haven't checked this, will report back.
    4. instantaneous MPG at constant speed: I'll have to check this explicitly under those conditions (tough to find highway flat stretches near Seattle though), but average highway mileage has been only a bit lower than usual (~43-45 mpg). Not sure about instantaneous since it fluctuates (few flat stretches) between ICE on/off.
    5. amps coming from MG1 and MG2: Unfortunately, I only recorded the HV battery data. I'll take a look at the engine data when I attempt the flat road test.
    Some other info that may help:
    • See the attached "screenshot 1". I recorded a drive around my neighborhood just to see what happens with the different HV battery measures. Notice how the SOC drops when at a stop (in D), going from 75% to 40% without pressing the accelerator (starts around 280s mark on the x-axis timeline). Is this normal? If not, what might be the causes?
    • Similarly, "screenshot 2" shows a 10% drop SOC within 2 minutes while powered on but with the ignition off (sorry, not sure what is the official name of this power state, with start button pressed twice without foot on brake). Is this normal? If not, what might be the causes?
     

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  4. Nat C

    Nat C Junior Member

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    Some more updates:
    • Did another brief in-city drive, and got some more weird symptoms. Let the car idle briefly upon startup which charged the HV (see screenshot). Then drove around briefly, after a couple minutes of which the SOC began to plummet all the way to 0%. I didn't think it was possible for the HV to discharge to that point??!!
    • I repeated this sequence two more times, but another drive this evening failed to get the initial charge. SOC sits at 0% (!!!).
    • Still no DTCs, but with SOC at 0%, I do get a warning about putting the car into N that the main battery will not charge.
    I'm not sure how to monitor amperage from MG1/2 going to the HV within Techstream. Do you happen to know?
     

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  5. Nat C

    Nat C Junior Member

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    Just bumping my own thread in case there is anyone out there who has seen this strange behavior. Techstream reporting 0% SOC, how is this even possible (while still running ICE, and without any DTCs or dash lights)??
     
  6. nh7o

    nh7o Off grid since 1980

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    Not normal, as you already know. It looks to me like there just isn't all that much battery capacity. When I sit in Park, with car in Ready mode, engine off, and no accessories or anything turned on save for the laptop running Prii-dash, the inverter and all the various ECUs in the car will create a draw of ~1.5A from the HV battery. At that load the SOC will drop slowly over 10 minutes, but not like what your graph shows.

    I see the battery temperature values look high for just having taken a short drive. 126F is rather too high for a healthy pack. You are not using the AC so the intake is at 92F, but it should not have diverged that far from ambient in 5 minutes. If the battery gets too warm, the HV ECU will limit limit the charging current. If you hear the battery fan running, this would be confirmation of overheating of the pack. (I run my batteries up to full charge all the time, and they show a bump in temperature due to the exothermal response of NiMH chemistry, but I don't see anything like 126F.)

    Do some more testing, perhaps try to make a graph of the battery temp. from cold start to the conditions shown in your last sceen shot.

    While 101K miles is too soon for this kind of thing, it is not impossible. I am not certain, and maybe someone can weigh in, but the high battery pack temp looks like the most likely symptom of battery failure coming soon.
     
  7. Nat C

    Nat C Junior Member

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    I think you are on to something with the high battery temps. At the start of this drive (but not during this particular recording), I did hear for the first time the high HV battery fan noise. Total drive time was ~45 min. but this included several stops with the engine off. Ambient air temp, as you note from the intake, was relatively high (90F). A quick look at this PC thread indicates that, indeed, 126F is considerably higher than expected though I'm not sure about the poster's driving conditions (if that could even account for such a large deviation).

    Attached is another set of screenshots from the same drive showing SOC %, one of the battery temp readings, and battery current. Tomorrow morning I'll try to get a recording from a cold start.

    I still can't believe that there haven't been any DTCs thrown—would make this diagnostic process a lot easier. I'm taking the car to the dealer tomorrow for a "free" battery test so maybe that will provide more info. I'm still absolutely puzzled by the 0% SOC reading—how is that even possible?

    One more question: do you think it's worth checking the battery cooling fan? I don't have pets and am generally pretty tidy with the car, but I'm less certain about the previous owner. Just trying to consider other causes of the high battery temps, and wishfully thinking it's not the actual HV battery.

    Thank you again.
     

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  8. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Wow, that's unbelievable there are no DTC's. When the SOC reads 0, does the car still start if you turn it off? If so, the SOC is not at 0. The car will not allow starting of the ICE if the battery SOC drops to 16% or less (to protect the battery). If that's the case, you may have a bad sense wire.
     
  9. Nat C

    Nat C Junior Member

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    Thanks for chiming in.

    Either something is wrong with my VCI/Techstream setup, or there is some computer/sensor error on the car itself. The ICE definitely starts while reporting the 0% SOC which, even with my limited understanding, just isn't possible.

    Is there any chance that the car would fail to prevent starting the ICE when SOC < 16%? Given that the car still starts, I think that the reported SOC must be inaccurate. But I also want to be sure that I don't damage the battery (if that hasn't already happened) by continuing to drive it.
     
  10. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    No, there is no chance unless it is receiving an erroneous signal or the software thinks its receiving an erroneous signal. The fact that you have no DTC's is telling. And... what its telling me is that you have no problems (other than your setup of course). :)

    Tell me how your "Energy" display (for battery state) is reacting? Is it following the Mini VCI readings? I'm guessing no.
     
  11. Nat C

    Nat C Junior Member

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    Actually, the MFD does seem to track the MVCI readings. At 0% SOC on the MVCI, it shows a single purple (pink?) bar.
     
  12. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Well, then its likely a sensor.
     
  13. nh7o

    nh7o Off grid since 1980

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    For myself, in this case I would open up the back and look at the fan and ducts for dirt. And I would open up the battery case and look for corrosion on the connectors and wires. It's not that big of a task for anyone comfortable doing simple car maintenance.

    I am sure the mVCI is fine, so this is something related to the battery and controls. If you can drive the car for 45 minutes, it would seem that the inverter and drive train are OK.
     
  14. slimothy

    slimothy Junior Member

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    One other thing you can monitor is the maximum current that you can get in/out of the battery. After warm-up getting 60 amps in the battery and 100 amps out of the battery should be possible; it definitely sounds like you can't get lots of current out of the battery.

    You may also find a much larger weak/strong voltage difference when requesting lots of battery power, and that may tell you if you have failing modules versus battery sensing/ECU issues.
     
  15. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    But wouldn't failing Modules cause a dtc to be triggered?
     
  16. Nat C

    Nat C Junior Member

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    Thanks everyone for your troubleshooting, very much appreciated. The added pressure for me is a planned road trip to Yellowstone in 1.5 weeks. Not figuring this out beforehand would leave me very uneasy about driving my Prius.

    slimothy:
    • Looking back at my screenshots posted earlier, it looks I was getting ~40A out of the battery with in-city driving (if I am reading that correctly, might have +/- reversed and/or might be looking at the wrong data).
    • Modules look pretty balanced to me—difference between max/min is between 0.1-0.2V including under discharge (in R with foot on brake).
    usnavystgc:
    • What sensor(s) or ECUs do you think might be the culprit? Hybrid Control ECU? Battery ECU? Other components? Other than swapping parts, would there be definitive ways of testing?
    nh7o:
    • Thanks for the suggestion, looks like I might have my Sunday morning activity planned for me. I saw some videos online, doesn't look too complicated as you indicate so I might have a go at checking the fan/ducts and battery.
     
  17. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    The more I look at this thread, the more I think your car is fine.
     
  18. Nat C

    Nat C Junior Member

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    Well, that's reassuring. But there is still the bizarre behavior with the 0% SOC—if I didn't multiple recordings of it on Techstream, I'd think I was going crazy.

    I'm currently neck deep in revealing the HV battery and, so far, nothing there either. Drove the car this morning and it exhibited totally normal behavior with the HV system. The inconsistency of the 0% SOC is both reassuring and incredibly frustrating. And with no DTCs, I doubt the dealer is going to uncover anything at all in their $114 diagnostics test.

    One more question: do any of you know what data set I should be tracking in Techstream to monitor the HV output current?
     
  19. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    I don't but, what will doing that net you? If it were wrong, it would trigger a dtc.
     
  20. Nat C

    Nat C Junior Member

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    Fair point, my only thought is that this is an ECU issue (since 0% SOC is not possible), but I would expect a defective ECU to trigger a DTC as well. It's probably quite obvious that I'm fumbling at the limits of my comprehension, just trying to figure out some way to understand or explain the weird SOC behavior.

    I exposed the battery this morning, visually inspected the terminals (some corrosion on 8 terminals but looked pretty minimal to me), and manually checked each cell with my multimeter. I also inspected the battery fan which only had minimal dust on the fins. End result: nothing of note.

    So this leads back to the sensor suggestion. Any advice on further troubleshooting that?

    Thanks again.