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P0A2D detail 249 Red Triangle

Discussion in 'Gen 2 Prius Main Forum' started by JohnStef, Jul 26, 2022.

  1. JohnStef

    JohnStef Member

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    I am trying to help a single mom, with a 2007 Prius.

    An interesting bit of info, when I clear the fault codes the dash is clear and turn the power off. When I power up the car there are no dash lights, as soon as it is put in drive and the engine starts it throws P0A2D/249

    From the service manual:
    DTC P0A2D/249 Drive Motor "A" Temperature Sensor Circuit High
    Open or +B short in No. 1 motor temperature sensor circuit
    • Wire harness or connector
    • Hybrid vehicle motor
    • HV control ECU

    The resistance of the thermistor, which is enclosed in the No. 1 motor temperature sensor, changes in accordance with the changes in the temperature of the motor. The lower the motor temperature, the higher the resistance of the thermistor. Conversely, the higher the temperature, the lower the resistance. The No. 1 motor temperature sensor is connected to the HV control ECU. The power voltage of 5 V is supplied from the MMT terminal of the HV control ECU to the No. 1 motor temperature sensor via resistor R. Because resistor R and the No. 1 motor temperature sensor are connected in series, the resistance changes with the changes in temperature of the motor, which causes the MMT terminal voltage to also change. Based on this signal, the HV control ECU limits the load in order to prevent the motor from overheating. Furthermore, the HV control ECU checks the No. 1 motor temperature sensor for a wiring malfunction and the sensor for a malfunction

    Anyone solved this?
     
    #1 JohnStef, Jul 26, 2022
  2. Tombukt2

    Tombukt2 Senior Member

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    So the motor thermistor is bad the whole transmission has to come out to get at it and you probably can't change it you have to change the motor to get the sensor just a guess.
     
    #2 Tombukt2, Jul 26, 2022
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  3. dolj

    dolj Senior Member

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    Open or +B short in No. 1 motor temperature sensor circuit
    • Wire harness or connector

    Did you check the wire harness or connect for an open or B+ short in the No. 1 temp sensor circuit?

    The diagnostic procedure in the repair manual will have the requisite steps to follow.
     
    #3 dolj, Jul 26, 2022
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    Really, follow the service manual diagnostic procedures. Early on I would give all the wiring underhood (to the connector on the trans) a good inspection for rodent damage.

    Look at scantool data for the hybrid control ecu to see what it reports for temperature reading.

    Otherwise I'd pop the lower glove box out to access the hybrid control ecu connectors and start doing resistance and voltage testing.

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, Jul 27, 2022
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  5. JohnStef

    JohnStef Member

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    Thanks dolj

    This level of repair is kind of daunting for me, I am used to finding a problem and replacing a part, plug and play. Here we have a mystery with several possibilities. My 1st question when reading the service manual description of this error code was "where IS this plug they refer to?" M10 No. 1 motor temperature sensor connector

    I found this image from an other poster in Prius chat:
    upload_2022-7-27_9-12-58.png
    This code description is from the Toyota service manual:
    upload_2022-7-27_9-36-40.png
    From my ThinkDiag scanner I have a voltage of 11.41 at +B as mentioned above from the service manual.

    At this point I do not understand what the 11.41V is telling me except that it is neither "open" or "GND short circuit" as referenced above in the screen shot.

    I'll check the plug for damage and that it is seated.
     
    #5 JohnStef, Jul 27, 2022
  6. Tombukt2

    Tombukt2 Senior Member

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    By looking at the picture of the sensor it looks like a standard screw in sensor temp type like that are all over other Toyotas and this car on the back of the head just a different type of fitting probably to go into the transmission bell housing I have a car here that's open I can pull that sensor and have a look and see if that is just the plug and a wiring actually goes to a separate sensor and MG1 and two or how that works or look up the individual part to see what it looks like before it's inserted I don't see how one sensor would read both mgs? But I guess it's possible
     
    #6 Tombukt2, Jul 27, 2022
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  7. JohnStef

    JohnStef Member

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    Inspection of the plug at the engine shows a red wire broken free. Very Happy to find a clear cause of the code. I will splice of a good plug and watch the dash light disappear!
     
    #7 JohnStef, Jul 28, 2022
  8. ChapmanF

    ChapmanF Senior Member

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    Yeah, that's what mr_guy_mann was getting at. There can be a code where the fortune cookie says something about some sensor, but it won't always mean you solve the problem by replacing that sensor. It means for some reason the signal from that sensor isn't getting to the ECU, and it's up to a human to find out why.

    Yes, if the motor temperature thermistor really were bad, you'd have to replace the transmission. But then, that thermistor is well protected inside the transmission, and thermistors going bad really isn't much of a thing, so a problem like this is nearly always going to have some other explanation, and when you find the right explanation, you win.
     
    #8 ChapmanF, Jul 28, 2022
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  9. JohnStef

    JohnStef Member

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    P0A2D/249 is clear, it had a broken red wire at the plug. I spliced in a new plug, very cramped but doable.

    With this clear P0A08/264 showed up. The troubleshooting list is daunting.

    With the car off the 12v battery reads 12.4v at the batter, with the car on it reads 14.15v. Does this show the DC/DC convert is ok?
     
    #9 JohnStef, Jul 29, 2022
  10. mr_guy_mann

    mr_guy_mann Senior Member

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    14V shows that the DC-DC converter can function. Toyota doesn't give you much in the way of specifics as to what the ecu sees in order to set that code. Does the code set immediately on ready?

    My thought is - there is no reason for a single wire out of 4 at the motor temperature sensor connector to "just break". If a critter nibbled 1 wire, then I would inspect all the harnesses going into the inverter.

    Posted via the PriusChat mobile app.
     
    #10 mr_guy_mann, Jul 30, 2022
  11. JohnStef

    JohnStef Member

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    A 3mm bare section at the end of the wire was exposed. The plug in question had the red wire pulled out, as if it was snagged hard. No chewing.

    Thank you mr_guy_mann for this comment and the one above.
     
    #11 JohnStef, Aug 1, 2022
  12. JohnStef

    JohnStef Member

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    mr_guy_mann I just went to the car to test for the condition you specified when the code shows up. I started my scanner (ThinkDiag+) and the car. While in park I cleared P0A08. This time it cleared and the red triangle stayed clear. Surprized and somewhat in disbelief I shut the car off and restarted, no red triangle and no code. I drove the car, torqued the motor in drive to put demand on the system, I scanned again, no code and no pending code.

    I am not a pro so I pray to God a lot and ask Jesus for help and guidance when I do these repairs, I cannot reasonably explain this in any other way. I am very thankful.
     
    #12 JohnStef, Aug 1, 2022
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