P0A3F error code in 07 Prius, only after car has been sitting.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Sam Brinson, Aug 30, 2021.

  1. Sam Brinson

    Sam Brinson New Member

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    Can anybody explain this? If I drive the car every day, it seems that I don't have any issues. But if I let it sit for a few days, then the P0A3F code will come on, oftentimes at a stoplight. I reset it with my BlueDriver reader, and it drives fine, but it is a pain.

    I just bought the car about a month ago, so I'm not sure the history. It has a Green Bean Battery in it that was replaced in 2019. I'm wondering if it doesn't hold a charge as well as an OEM one or something, and that may be why the code is there after a few days of it sitting. Any other ideas?
     
  2. dolj

    dolj Senior Member

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    It looks like something is going on with the transaxle.

    DTC:
    P0A3F (INF 243) Drive Motor "A" Position Sensor Circuit
    DTC Detection Condition: Interphase short in motor resolver circuit
    Trouble Areas:
    • Wire harness or connector
    • Hybrid vehicle motor
    • HV control ECU
    DESCRIPTION

    The motor resolver is a type of sensor that detects the position of the magnetic poles, which are indispensable for ensuring the highly efficient control of the MG1 and MG2.

    The stator of the resolver contains an excitation coil and two detection coils. Because the rotor has an oval shape, the gap between the stator and the rotor changes as the rotor turns. An alternating current with a predetermined frequency flows through the excitation coil, and detection coils S and C output alternating currents in accordance with the position of the sensor rotor.

    The hybrid vehicle (HV) control ECU detects the absolute position of the rotor in accordance with the phases of detection coils S and C and the height of their waveform. Furthermore, the CPU calculates the amount of change in the position within a predetermined length of time, in order to use the resolver as a speed sensor.

    MONITOR DESCRIPTION

    The HV control ECU monitors the motor resolver output signal. If the HV control ECU detects output signals that are out of the normal range or specification, it will conclude that there is a malfunction of the motor resolver. The HV control ECU will illuminate the MIL and set a DTC.
     
  3. ChapmanF

    ChapmanF Senior Member

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    I could picture here something like resolver wiring that's been compromised in some way that's humidity-sensitive, where driving regularly keeps it warmed and dried out. Something like that.
     
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    I would absolutely verify that is the true code being displayed. I'm not familiar with the BlueDriver system, but there have been instances of generic readers 'misreading'.
     
  5. ChapmanF

    ChapmanF Senior Member

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    I don't think it's very easy to 'misread' a DTC; they are encoded in a pretty simple way, and a reader does not need to know anything about what the code means, just to be able to display the five-character code correctly.

    There was such an error in the Dr. Prius app versions before mid-August, reportedly now fixed. As it would almost have to, that seemed to involve a simple, deterministic mistake in the decoding; if you knew what the app was doing wrong, you could look at the bogus code it displayed and work out what the real one was.

    P0A3F is definitely a valid Prius code.
     
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    I have read somewhere that the connector on the transaxle for the resolver wiring is "delicate" and is "easily damaged". I might think the OP should go over the diagnostic chart for that code- it's fairly easy to drop the glovebox, unplug the harness from the hybrid ecu and ohm out all the resolver circuits. (and check for high resistance shorts between all the circuits- and ground).

    Posted via the PriusChat mobile app.
     
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