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Need help diagnosing P0AFC

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by SB6, Dec 3, 2022.

  1. SB6

    SB6 Member

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    Would appreciate some help figuring this out. A couple weeks ago, my 2010 threw DTC P0AFC. There were a few other codes (C2175, C1202, C1256, C1259, C1310, U0155), but I'm thinking they're all just random codes triggered by whatever is causing the P0AFC. Not sure what the U0155 is, I've seen that a lot on and off over the years without noticing any actual issues.

    Anyways, I checked my battery voltages using Dr. Prius and Techstream, and it's showing Block 04 at 0.00V, and Block 05 at nearly 25V. Trying to figure out if I just have two bad cells, or if something else is going on. If it's just two bad cells, why would one suddenly drop to 0V while the next jumps to 25V?

    The car seems to drive okay, it's just the ICE is constantly running.

    Here are some screenshots:


    Any ideas or diagnostic suggestions?
     
  2. PriusCamper

    PriusCamper Senior Member

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    Something has lost connection/unplugged...
     
  3. ChapmanF

    ChapmanF Senior Member

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    The C1259 and C1310 are definitely because of the P0AFC, but they are not even the tiniest bit random. Those are the codes the brake/skid ECU sets for the exact purpose of telling you to go look at your power management control ECU code(s).

    C1202 and C1256 are not related to the P0AFC. They are just two other problems your brake system happens to have. One is with the sensor for the fluid level, and one is a problem keeping the brake assist pressure pumped up.

    C2175 is an issue with the tire pressure monitoring system.

    U0155 is a communication error: something in the car can't communicate with the combination meter. It would be helpful to know what can't communicate with the combination meter. As you have Techstream, you can find that out, just by paying attention to which ECU the U0155 code is being reported for.
     
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  4. mr_guy_mann

    mr_guy_mann Senior Member

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    There's a broken voltage sense wire somewhere between the stud at the battery module and the ecu.

    Posted via the PriusChat mobile app.
     
  5. SB6

    SB6 Member

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    Not sure why the tpms might be throwing a code, as I just had all 4 sensors replaced while getting new tires...

    As for the U0155, if you look at the screenshot, it's the Smart Key ECU reporting the code.

    Hmm okay. Since I'm going to have to dig in to the battery and look for a bad connection, is there anything else I can take care of at the same time? From what I've seen, I can clean the bus bars and the battery fan. Anything else?
     
  6. ChapmanF

    ChapmanF Senior Member

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    Those voltage sense wires don't connect directly to the power management control ECU; they connect to a little box back in the battery itself called the "battery smart unit" or "battery pack sensor module", and that little unit then sends the readings over a serial link to the power management control ECU.

    P0AFC is not so much a code about any of the sense wires, as about the little smart unit itself detecting an internal malfunction and reporting that. There are seven pages in the repair manual for troubleshooting it.

    C2175 means the tire pressure monitor ECU either isn't getting the vehicle speed sensor signal, or from the receiver antenna it isn't getting all the expected IDs and signals from the four transmitters. There are four pages in the repair manual for troubleshooting it. If the latest thing that happened was replacement of the transmitters, maybe something didn't go perfectly there, such as registration of all their new IDs. (It's also always possible that something else just coincidentally went wrong.)
     
    #6 ChapmanF, Dec 3, 2022
    Last edited: Dec 3, 2022
    SB6 likes this.
  7. SB6

    SB6 Member

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    Do you happen to have page numbers for P0AFC? And C2175 as well, but I think the more important thing right now is the P0AFC.

    Also, I just looked again, and it's actually P0AFC-123.

    Also figured out how to PDF the freeze frame data. I've attached it here, if anyone can help me interpret it.
     

    Attached Files:

    #7 SB6, Dec 3, 2022
    Last edited: Dec 3, 2022
  8. ChapmanF

    ChapmanF Senior Member

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    Right, that's a P0AFC with subcode 123.

    But I don't think P0AFC has any other subcodes besides 123, so the subcode isn't adding a whole lot in this case.

    I'm not looking in a dead-tree version of the manual, so I haven't really got page numbers sure to match up with anybody else's. If you have a PDF available, it's easiest to just do a search for the code; sometimes you need to 'next' several times past hits on other pages that mention the code, until you come to the page devoted to the code itself.

    If you do have a printed version (possible for 2010, I think it was 2011 they discontinued those), flipping through with your thumb, looking for the codes at the tops of the pages, usually works.
     
  9. SB6

    SB6 Member

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    Found it. Pages 3817 - 3823 of 7595. Will have to take a shot at this.

    @ChapmanF Thank you for pointing me this way. I'm still lost, but not completely lost anymore :LOL:
     
  10. SB6

    SB6 Member

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    What is the Universal Trip the repair manual says to perform after clearing codes?
     
  11. ChapmanF

    ChapmanF Senior Member

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    It's kind of a standard five minute trip that is part of the confirmation driving patterns for a lot of different codes, so instead of repeating it a whole bunch of places, they just put the details one place up at the front of the section, where permanent codes are explained.
     
  12. SB6

    SB6 Member

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    Any tips on removing relays from the fuse block? Trying to remove the IGCT relay to test, but haven't managed to take it out.

    I popped off the plastic cover for the relay, but not the actual relay... Not sure that was supposed to happen
     
  13. SB6

    SB6 Member

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    Nevermind. I removed the two relays under it, and was able to finally get the IGCT relay off. Damaged the plastic clips for the plastic cover, though, so that could be an issue in the future.

    I do need help deciphering my measurements, though
    [​IMG]


    Code:
    https://imgur.com/a/TpVv89N
    According to this (pg. 3821 of 7595), I should get under 1 ohm when I measure across 3 and 5 without 12V applied across 1 and 2. I get 0L (infinite resistance/no connection, unless I'm mistaken). With 12V across 1 and 2, it says I should get over 10kOhm, but I get a click and continuity/0 Ohms. Additionally, with no voltage applied, I measured about 170 Ohms across 1 and 2. What am I doing wrong?

    There's a DIM/DRL relay near the IGCT relay, and they seem to have the same part # so I did the same test on that one, and got the same results...

    Actually, my test results make sense to me, and indicate a good relay in my opinion. The test conditions don't make sense to me, and seem opposite from what it should be... If there is voltage between 1 and 2, then the switch should close between 3 and 5, meaning continuity/0 resistance -- which is what I got. With no voltage, the switch should be open, meaning infinite resistance -- again, what I measured. But why would the repair manual be saying the opposite??
     
    #13 SB6, Dec 11, 2022
    Last edited: Dec 11, 2022
  14. ChapmanF

    ChapmanF Senior Member

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    I agree that looks like a mistake in the edition of the repair manual you are looking at.

    If it is still that way in the up-to-date repair manual found here:

    Toyota Service Information and Where To Find It | PriusChat

    then someone should report it. I did report a mistake in the manuals one time using the link they provide online, and they did follow up on it.
     
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  15. pancake

    pancake Junior Member

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    Hey! I have the P0AFC-123 code after replacing the 12V battery, but the dealership won't tell me anything other than that I need to pay for another diagnostic.

    Have you been able to find the solution to your P0AFC-123 code? On my car this is (apparently) the only code that I am getting. Car still has the READY light on, but the hybrid battery still has a charge and doesn't charge when moving...
     
  16. SB6

    SB6 Member

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    Not yet. I haven't had a chance to open up the battery to take look at the wiring harness or smart battery unity, but I'm 70% certain my issue is going to be corroded pins on the smart battery unit, in which case I can hopefully just replace that one unit.
     
  17. SB6

    SB6 Member

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    When the repair manual says to check voltage on the IGCT in step 1 (CHECK HARNESS AND CONNECTOR (IGCT VOLTAGE)), do I disconnect the connector and check voltage? Or do I poke around for bare wire to check voltage with everything connected? Kinda confused here

    Page 3819 of 7595
     
  18. ChapmanF

    ChapmanF Senior Member

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    You measure the voltage in step (f), and none of the steps (a) through (e) said to disconnect the connector. The illustration shows test probes poked into c1 still connected, and the whole thing has note *1 in the illustration, which is given as "Component with harness connected."
     
  19. SB6

    SB6 Member

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    Hmm I don't see the probes in the illustration, but yeah that makes sense. I'll have to figure out how to get my leads in that way.

    A couple other things that are unclear to me from the repair manual:
    • When it says to disconnect or connect the cable from the negative battery terminal, it's talking about the 12V battery, right?
    • In step 4 (CHECK HARNESS AND CONNECTOR (IGCT RELAY - BATTERY SMART UNIT)), I'm checking the resistance between the c1 connector and the IGCT relay terminal, not the relay itself, correct? So like the terminal in the fuse block, not the blade on the relay? Just making sure. In that case, I'd need pretty long wires on my test leads... or just extend them with like alligator leads or something I guess?
     
  20. SB6

    SB6 Member

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    I really can't figure out how to measure the voltage with the connector still connected. There's not much space there where the individual wires go into the connector. Definitely not enough space for my multimeter's test leads. I tried with paper clips, with alligator clips in between my test leads and the paper clips. I'm not sure that the paper clips are making actual contact with the wires, though, as I'm not getting much in terms of voltage readings