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Check Engine / Hybrid Battery Sensor Failure / Code: P0A9C

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by alexanderchristiansen, Jul 10, 2017.

  1. alexanderchristiansen

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    Hi PriusChat.

    I am so thrilled to find this amazing forum.

    I bought a Prius 2005 with around 125K miles on it 2 months ago - and until now I have loved it with all my heart! I was specially thrilled when I managed to do the chicken dance
    I have put around 3K miles on it and unfortunately I got myself a red triangle with a “!” in the middle.

    I took it to a mechanic for a scan and the errorcode was:
    P0A9C: Hybrid Battery Temperature - Sensor "A" Range/Performance

    Apparently there’s a sensor causing some temperature shifts that’s not too good. He then also found out that I was looking at a Hybrid battery that was having a hard time on a few of the modules - and ended the conversation with: “You need a new hybrid battery!”.

    To be frank I would really like to find another solution than buying a brand new battery. So I was hoping to find some help in here on what to do. I paid 5K for the car and know that my time here in the states might be limited to max one year from now - whereas I then have to sell the car again.

    I got a lot of paperwork now with diagnostics on the errors - I could potentially upload this if that could be of help for any one of you guys - let me know.

    My question is:

    Could I potentially try just to get the Sensor replaced? Is the risk of it not working too high? And would the cost of labor be too expensive compared to the chances of it working?

    I was further thinking of changing the modules - simply because it’s too pricy for me to pay 3K USD for a new battery? But would it be smarter to buy a used hybrid battery (with +20K mile warrant on it)?

    It gives me around 40 mpg right now.

    Bonus info:
    My girlfriend drove it the other day and told me that out of a sudden the car had a serious rough time accelerating and in that moment started to sending a lot of air through the air vents (do not know if this the right word) on the back seat. (The aircondition air vents)

    It stopped when she turned the car off - but we haven’t really been out driving since.

    Best Regards,
    Alexander.


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  2. fotomoto

    fotomoto Senior Member

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    A loud fan from the rear seat is yet another sign of a battery failure. The car has probably thrown more codes now since the GF drove it.

    Sounds like you already know your options. If only needed for one more year, I'd go the rebuilt battery option from a reliable, local source who will honor their warranty because they can/will fail too. I'd check with Luscious Garage | Hybrid Specialists there in the bay area for their recommendation.

    GOOD LUCK!
     
  3. JC91006

    JC91006 Senior Member

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    If you were here in SoCal, I can probably fix that up for you for a low cost. If you're only looking for 1 year, it shouldn't be too hard to get a rebuilt to last a year. Beyond that would be the unknown.
     
    SFO likes this.
  4. JimN

    JimN Let the games begin!

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    Welcome to the site. I'm not one of the battery experts but I don't believe the issue is a faulty sensor.

    I agree with fotomoto that the symptoms you describe point to a failing battery.

    Since the battery only has to last a year a refurb Dorman purchased through an auto parts store may be a reasonable alternative to a brand new battery. Read and understand the warranty before the purchase to ensure you are covered.

    Luscious Garage does have a good reputation so contact them since you are local.
     
  5. dolj

    dolj Senior Member

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    I agree with both these statements.

    The code does not mean that the sensor is broken, it more likely means the component the sensor monitors (or the wiring between the sensor and the ECU) is flakey, and the repair manual will give the work up to further diagnose where the problem is.

    Given the other information you have given, it leans toward the HV battery failing.

    Options are getting a minimal repair done by someone (trustworthy) like JC91006 above, to get you through. Getting a complete battery replacement from a repairer/rebuilder is getting to be a crapshoot (6 month - 3 years) there days, as the pool of usable old modules gets scarcer and scarcer. Also too many charlatans getting into battery repair. The best of breed repair is a complete new battery from Toyota, but given your personal circumstance may not make complete sense as you will not get the total benefit from going that route. You are in a precarious situation, unfortunately.
     
  6. Pschwind

    Pschwind New Member

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    I have a 2007 Prius, approx 175,000 miles. Replaced hybrid battery approx 1 1/2 year ago with a new Toyota hybrid battery. 12 volt battery replaced 3 weeks ago. Yesterday had red triangle with ! And check engine light. After checking for codes first time no code. Checked oil, slightly low, added small amount of oil. 2nd time of checking code, it is P0A9C, hybrid battery temperature sensor circuit. No notice of power issue, car seems to be running well. Any ideas of what the issues is??
     
  7. Raytheeagle

    Raytheeagle Senior Member

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    Welcome to Prius Chat (y).

    There are temperature sensors along the battery, so one might have a loose wire or connection issue.

    If you’re pulling the code, what device are you using to do so?

    Can you see the temperature it is reading?

    Good luck and keep us posted (y).
     
    SFO likes this.
  8. JC91006

    JC91006 Senior Member

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    Check if there is fluid movement in the inverter coolant reservoir, open the cap while the car is in READY. No movement would mean pump failed
     
  9. khan209

    khan209 New Member

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    I have 2005 Prius and after rebuilding the hybrid pack i broke one wire from temperature sensor by the clip. took it out sorted with wire put it back but getting the same error code. P0A9E, any help would be highly appreciated since its hard to find the part.
     
  10. HowardK

    HowardK Junior Member

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    OK, my 2 cents worth. First you have to buy the techstream program from Ebay. Next, you can see each individual cells voltages in the hybrid battery. There are 2 modules per cell. Once you determine which cells are bad (usually a volt or more lower) you have to disassemble the battery and remove the jumpers(copper plates) from both sides of the battery and test each individual module in that cell. Youtube has a few videos on this. Ebay has good used modules for cheap. I use a setup to charge and discharge each individual module 5 times. The turnigy charger I use discharges down to 6v, then charges up to delta peak(Capacity), or full, which is not the same. You are wanting to cycle discharge/charge until every module says capacity. This is usually done by the 5th discharge/charge cycle for most modules. I usually let the battery sit for at least 24 hours and re-check voltages, any deviation in voltage is suspect. My first rebuild has lasted for 5 years and is still going strong. Any naysayers are just trying to sell you something. This is not rocket science. The temp sensors you are referring to are on the bottom of the cells I think there are 4? Be careful when replacing modules, you may break the wire to the sensor! I hope this helps somebody!
     
  11. dolj

    dolj Senior Member

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    Great post, thanks for sharing.

    Just a note on terminology, there are six cells in a module and two modules in a block. In a Gen 2 battery, there are fourteen blocks or twenty-eight modules for a total of 168 cells.

    it is important to use the correct terms so that you are clearly understood and misinformation and/or confusion is minimized. It can be confusing for noobies to get to grips with the information when incorrect terms are used.