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P0A0D to no end…

Discussion in 'Gen 3 Prius Technical Discussion' started by Awells80, Jul 15, 2024.

  1. ChapmanF

    ChapmanF Senior Member

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    Good, there our manuals agree. That's the step 16 test, where OK ► replace power management control ECU.

    Back in your post #13, you had only mentioned the NG result for step 7 (where NG ► do step 16).

    Now we're back on the same page.
     
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  2. Awells80

    Awells80 Junior Member

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    I see what you are saying about my post #13. Now that we are on the same page, I’m having a hard time understanding why the diagnostic process has left me dry. I have replaced the Power Management Control ECU and I am left with the same results, meaning there is something more involved that is not in agreement with the rest of the system.

    Today, I performed insulation resistance tests to ensure there was minimal leakage current in the system. All my results were exceptionally high, indicating excellent insulation with no electrical leakage at the hybrid battery.
     
  3. Awells80

    Awells80 Junior Member

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    I think maybe I’ll go do a load test on all of my modules the way they sit right now and see what I come up with. I do not know.
     
  4. ChapmanF

    ChapmanF Senior Member

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    If you still have P0A0D, it just means there is something trickier going on with the dead-simple series interlock circuit that we didn't catch on the first pass.

    With the replacement power management control ECU in there, what is the step 7 test result now? That's the one that was NG, with the reading much lower than 10–14V, before you replaced the ECU.
     
  5. vvillovv

    vvillovv Senior Member

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    I know there's already be a hundred or two posts in this thread if you only asked one question pre post.

    What are you using to cycle and load test your modules?

    Back at the very beginning of this thread after you put your pack back into the Lexus. The fan stayed on for the entire time the car was on. My first thought was the packs re assembly.

    Than you add that you serviced the EGR. OK. I guess I'll assume this is the first time for both those services>
     
  6. Awells80

    Awells80 Junior Member

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    I definitely agree with ya. Something trickier is holding me back, but I’m not sure just yet, but I will figure it out with no doubt perhaps with a little bit of guidance and advice from the hybrid community. I went ahead and took pics of my notes from today So here’s the rundown for today that I’ve been working on, But first, to answer your Question about step 7, My voltage reading for that step was 5.7 Volts today. About 20 min ago to be exact.

    I started the day with a load test on all the individual modules, just for my own peace of mind. I used a 65 W headlight bulb for three minutes Per module. Attached are my results. I was kind of just throwing them down there, so hopefully they’re not too messy to read. Same goes for the P0A0D diagnosis steps I went ahead and wrote down. I’m newer to these vehicles and I’ve learned a lot. They are a whole new breed to me but I love learning about the way the systems work so far!

    I have my SC300 that’s not practical for daily driving that I’ve completely built myself set aside from the machine work on the engine and the Tig welding for the IC and 4” exhaust. I run E85 and yeah anyway, back to the subject at hand.
     

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  7. Awells80

    Awells80 Junior Member

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    To answer your question about the fan running at all times, there happens to be 2 identical plugs 3 or so inches apart. One going up the side panel an to the front of the vehicle, and the other going down to the charcoal canister. I had them swapped!!! Why and who decided this was a good idea I’ll never know, but I should’ve looked a little closer I suppose. Thanks for asking.

    For the load testing, I use 2 alligator clips fused to a 65w headlight bulb and 2 alligator clips for my multimeter as well timed for 3 minutes. I have done this an hour after grid charging the pack and I’ve also done this a week after letting it sit, (grid charge as well.)
     
    #27 Awells80, Aug 5, 2024
    Last edited: Aug 5, 2024
  8. ChapmanF

    ChapmanF Senior Member

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    OK, so that was the NG result that led you to step 16, where you checked the resistance between A62-35 and A19-32 and found it to be good (below 1Ω), leading to replacing the ECU.

    However, with the ECU replaced, you still have an NG result for step 7. Changing the ECU did not fix that.

    This is where it becomes important to read troubleshooting steps actively, as if you are following along in the reasoning of the engineer who wrote them.

    In step 7, you have unplugged A62 from the inverter, so none of the interlock circuit within the inverter or back to the battery is in play. You are simply testing the far end of a wire that's attached to A19-32 at the ECU.

    The ECU is the source of 12 volts onto that wire, which therefore should read as 12 volts to body ground when you measure at the A62 end. But the mere act of attaching your voltmeter pulls that voltage down by about half.

    That would make you think there is quite a high impedance in there somewhere: either in the voltage source within the ECU itself, or within that length of wire from A19-32 to A62-35 (or in that A19-32 pin-to-socket connection). A typical voltmeter has an impedance in the megohms, so for that to pull a voltage down by half, you'd expect to find a similar impedance of megohms either between the ends of that wire (a wire break or near-break), or in the ECU itself.

    So the next easy thing the engineer had you do was disconnect the other end of that wire and measure the wire's resistance end to end. You got under 1Ω, so the wire looked good. The manual then, following the most-likely explanation for all that, said "there's a high impedance here that can only be in the wire or the ECU and doesn't seem to be in the wire, so swap the ECU."

    Manuals are written to follow the most-likely explanation because it's, well, most likely. But here you've put in a different ECU and still have the same halved voltage reading at the far end of that wire. You still have the problem quite narrowly boxed in—no possibility other than that wire, those connectors, or the ECU (again!)—but haven't pinned it down yet.

    Do you own a set of backprobes? I'd be inclined to leave A62 disconnected (as in step 7) and backprobe A19-32, and measure the voltage to ground at that point. Is it more like 12 then, or already pulled down to 5.7?

    If it's already pulled down, I would next want to measure the voltage to ground that this ECU puts out on that pin with that wire disconnected. This may not be as simple as just unplugging A19 and measuring from that ECU pin to ground, because A19 might carry other things the ECU needs (like power). So it might mean backing terminal 32 out of connector A19, so you can plug the rest of A19 back into the ECU and then poke a probe in where terminal 32 went so you can measure from the ECU pin to body ground.

    You can see why further tests like these weren't in the manual—99 and 44/100ths percent of the time, if you measure low voltage at A62-35, you're going to spot an obvious high wire resistance in step 16 or have a bad ECU output.

    You just happen to be in one of those situations proving that weirder stuff in nature can sometimes happen. The manual can't really try to have every troubleshooting procedure include extra test steps to cover all the super unlikely weird cases, 'cause it's already 7000 pages long as it is. But this is where the active reading comes in, because once you've looked at step 7 and step 16 and understood what the engineers were telling you there and why, now when you find yourself in a weird case those two tests didn't get to the bottom of, you can think out what your next tests have to be.
     
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  9. Awells80

    Awells80 Junior Member

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    Firstly, Thank you for your detailed troubleshooting steps.

    Everything you stated sounds right on point, but just to clarify, In step 16, after verifying good resistance (below 1Ω) between A62-35 and A19-32, I replaced the ECU. However, I still have an NG result for step 7. The ECU replacement did not resolve the issue.

    In step 7, when A62 is unplugged from the inverter, I tested the wire from A19-32 to A62-35. The ECU is supposed to provide 12 volts on that wire, but connecting the voltmeter pulls the voltage down by half is what you are saying may be possible, indicating a high impedance somewhere between the ends of the wire or within the ECU. Although, the multimeter I use has a LoZ mode in order to apply a lower input impedance to the measurement circuit,

    After disconnecting the wire, I measured its resistance end to end and got under 1Ω, so the wire seems fine. The manual suggested replacing the ECU as we already know but I like where you are going with the idea of getting a voltage reading at the beginning of A19-32 connector while plugged in. A62-35, unplugged. I feel like that would work just fine, so we will find out soon enough, as it would narrow down one more thing.

    thank you sir for your help and advice with this.
     
  10. Awells80

    Awells80 Junior Member

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    Today, I conducted a few tests. Initially, I left everything connected and tested the voltage from pin A19-32 of the power management control to ground with the ignition on. The results were the same as when I tested from the A62-35 connector to ground with the ignition on. This consistency was expected, but it's good to confirm.

    Next, I reinstalled the replacement power management control to check for any differences. Again, with the ignition on and testing from A19-32 to ground, the results remained unchanged. I also tested with the interlock both engaged and disengaged, without touching the brake pedal (without trying to put the car in "ready" mode). As anticipated, this had no impact on the voltage readings.

    I also checked the resistance on the interlock switch between the two main power supply pins, and it measured 0.1 ohms.

    Interestingly, I decided to see what would happen with the ignition completely off. In this state, I measured 1.4 V from A19-32 to ground. When I switched to resistance mode, it started at about 15 ohms and gradually dropped to 7 ohms. The first two attachments show the readings with the ignition off, while the third attachment shows the voltage reading with the ignition on.

    I’m going through ideas in my head of what I could test for. If anyone wants to chime in, am all ears at this point!
     

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    #30 Awells80, Aug 6, 2024
    Last edited: Aug 6, 2024
  11. rjparker

    rjparker Tu Humilde Sirviente

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    I think your problem started with a diy battery rebuild and is likely to be resolved there. I assume no Ready is still a problem. Do the battery voltages still read incorrectly with Techstream? Absolutely sure the orange disconnect is pushed in, snapped closed and then pushed sideways?

    So you had at least one user induced error. I would verify what damage could have occurred when fan power was sent to the wrong place and vise versa.
     
  12. ChapmanF

    ChapmanF Senior Member

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    Keep in mind that when A62 is unplugged, as in the test step #7, nothing in the traction battery is in the picture. The service plug/interlock switch is out of the picture. The inverter cover interlocks are out of the picture. The inverter to battery wiring is out of the picture. Step 7 is testing, in complete isolation, the ILK output of the ECU and the wiring from there to the inverter, and nothing else.

    So in post #30, the voltage has been confirmed also low at the ECU end (pin A19-32). Still with A62 unplugged, right?

    It's about more than confirming an expectation, but finding something out. it could also have happened that you measured 12 volts at that point, which would have meant a high impedance had to exist between the ends of the wire (an intermittent one, as you measured < 1Ω in step 16).

    But having measured the same voltage at this end, you have largely ruled that possibility out. It remains to test whether the low voltage is seen on the ECU output pin with the wire disconnected (that is, terminal A19-32 backed out of the connector shell, as I suggested in #28).

    For this, too, I don't really have a prior expectation. It will either be the case that the ECU always outputs a low voltage on that pin, or that it outputs 12ish volts when no wire is attached there and is only pulled down when the wire is attached. The two outcomes are both possible and would tell us different things, suggesting different next steps.

    That's the next thing I'd test.

    The low voltage on ILK has been seen now with two different ECUs. Just so I have the order of events straight, was the replacement ECU tried only after discovering and correcting the connector mixup at the back of the car? Or could both of those ECUs have been in the car at times when the connectors in back were still mixed up?
     
  13. TMR-JWAP

    TMR-JWAP Senior Member

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    I tried following through this thread, but just a bit of clarification..
    Was the car working at any point prior to battery disassembly?
    Did you do any work at the inverter?
    When you installed the safety interlock socket/cable assembly, did you plug in the small connector to the interlock socket?
    When you installed the orange safety switch, you performed all three steps? Insert, rotate handle, slide handle sideways to push jumper wire into the interlock plug?

    I've seen many times where a DIY rebuild goes haywire because the small wire was never plugged back into the interlock switch socket, so the car would always think the safety switch wasn't installed. I think on the Gen 3s, there's also brown plastic resister (or whatever) mounted below the safety switch. I don't remember if they use similar connectors, but it may be worth checking that you've got them in correct positions..
     
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  14. ChapmanF

    ChapmanF Senior Member

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    Keep in mind that the OP's diagnosis has already proceeded as far as step 7 in the P0A0D troubleshooting, at which point everything in the back of the car (in fact, everything except the power management control ECU and the wire from it to the inverter) is eliminated from the picture.
     
  15. Awells80

    Awells80 Junior Member

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    Yes, the no ready Is still a problem. Techstream reads the voltages Just fine now. That was when those two plugs were swapped. After correcting my mistake, communication with the ECU code is gone and the voltages read as they should.

    The orange plug is as it should be. slid all the way over and all that and tested with the multimeter just to make sure. Battery reads full voltage when the switch is closed. Tested for the ILK/Ground plug as well. Also, Resistance at the 2 main terminals on the orange safety switch = .1 ohms.
     
  16. Awells80

    Awells80 Junior Member

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    Yes, that is correct.


    both of those ECUs were in the car during the time of the connector mixup.

    I happen to have a third…
    The boards have no VISUAL damage. I know this does not exempt either to be at fault.
     

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    #36 Awells80, Aug 6, 2024
    Last edited: Aug 6, 2024
  17. Awells80

    Awells80 Junior Member

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    yeah, the car was working. The hybrid battery code would come up every once in a while, but the main draw was when I was going through a car wash that pulled me through in neutral. I’ve never done any work at the inverter besides testing. The interlock is installed correctly. Same as the.ILK Signal plug. Thank you for asking

    We are good there. I’ve actually checked for continuity from the 2 wire connector in the back (ILK wire) to the converter up front and we’re good.
     
    #37 Awells80, Aug 6, 2024
    Last edited: Aug 6, 2024
  18. TMR-JWAP

    TMR-JWAP Senior Member

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    Yikes. Going through those "neutral" car washes is very risky. The car will not charge the HV battery while in neutral, so a moderately weak/aged HV battery and running the AC will likely cause the car to code out.. If it must be done, make certain the AC is off. That will give the HV battery a fighting chance, even if it's relatively weak. I avoid those car washes.

    I've never had a problem like this NOT be local to the battery, or where the most recent work was performed, whether it be a broken wire, broken safety switch, or missed connector. I'm not a big believer in coincidental failures. I happened to have a tote in the shop with the majority of parts from a 2013 CT200H HV battery. This photo shows the parts I was talking about. The two connectors I mentioned are nearly identical, but not. It appears the image flipped upside down, but it works I suppose.

    harness.jpg
     
  19. Awells80

    Awells80 Junior Member

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    Yeah man I had the stereo loud, A/C full blast.. and then.. barely made it out of there and all freaked out!
     
    #39 Awells80, Aug 6, 2024
    Last edited: Aug 6, 2024
  20. Awells80

    Awells80 Junior Member

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    So I wanted to share that I ended up using the lightbulb, discharging method the wrong way. I have read that it’s crucial to screw the bulbs in to start the discharging process. Well, The way I did it was, I made my harness with 2 200w bulbs, and then with the safety switch unplugged, I hooked everything up with the lightbulbs installed and all, and flipped on the Interlock switch. It clearly states to do otherwise on this prolong site. my question is, what could the results have done on my car? The interlock switch?
     

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    #40 Awells80, Aug 10, 2024
    Last edited: Aug 10, 2024