New to me owner with red triangle

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by sandmanx, Jun 22, 2026 at 11:05 PM.

  1. sandmanx

    sandmanx New Member

    Joined:
    Monday
    2
    0
    0
    Location:
    Texas
    Vehicle:
    2009 Prius
    Model:
    II
    Hello everyone. I picked up a 2009 Prius a month ago with 272K miles on it, and now I have close to 275K miles. When I was driving the car on Saturday back from my nearest town(I'm in rural Texas), it all of a sudden threw up a red triangle about 4 miles from home, and I limped it home and parked it. It won't start up now, and using the OBD Fusion app on my phone I am reading these codes: P0137(an oxygen sensor, it threw this on Thursday last week and I haven't gotten a replacement ordered yet), P1121(it's been on and been low priority) and P0AA6. It seems that my app can't read the sub code on that last error and I think that's what's causing the issue. What would be the best move from here to get it back up and running? I typically do my own mechanical work and I'm experienced with DIY off grid solar for my house setup for what's that worth.

    Thanks
     
    #1 sandmanx, Jun 22, 2026 at 11:05 PM
  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    28,551
    18,895
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    The P0AA6 is why the triangle is on, yes.

    The INF code just saves time in your diagnosis by placing the fault in one of these four areas, so you don't waste time looking for it in the other three.

    [​IMG]

    If you aren't at all able to get your hands on a scan tool that shows you the INF code, you can still find the fault, it's just more work.

    You can look for threads on how gen 1 owners had to proceed (they didn't have the handy INF codes yet, and the code was P3009 in that generation, because SAE hadn't standardized P0AA6 yet). You'll have to adapt what you find there a little, because gen 1 didn't have electric air conditioning (the INF code 611 area).

    Oo, I didn't realize 'til now there's also a Carolyn Coquillette video about that. You're in good hands now.

     
    #2 ChapmanF, Jun 23, 2026 at 8:06 AM
    Last edited: Jun 23, 2026 at 8:18 AM
    sandmanx likes this.
  3. JC91006

    JC91006 Senior Member

    Joined:
    Nov 10, 2013
    16,925
    8,637
    0
    Location:
    Los Angeles, CA
    Vehicle:
    2008 Prius
    Model:
    II
    At 272k miles when you bought it, these cars usually will have problems. If you were able to drive 3k since, I am guessing your most likely cause to be a bad Hybrid Battery causing that error. A leaking module inside the battery. But that's just a guess, at your mileage it could be anything that's causing that (transaxle, AC, battery, inverter)

    When you get this error, you can start the car once before it disables itself again. To start it, you would have to disconnect the 12v battery and erase the code. Once erased, the car will start 1 time. If you need to move the car, that's the method you would use.
     
    #3 JC91006, Jun 23, 2026 at 10:18 AM
    sandmanx and Brian1954 like this.
  4. sandmanx

    sandmanx New Member

    Joined:
    Monday
    2
    0
    0
    Location:
    Texas
    Vehicle:
    2009 Prius
    Model:
    II
    It looks like this may have been super simple. I went to pull the 12v terminal connector off and it was super loose. I restarted and was able to move and start/stop it multiple times. I'm going to see if I can find a replacement tomorrow when I go to the auto parts store. The problem happened immediately after hitting a large pothole on a dirt road so that seems plausible.
    I know it has a boatload of mile, but everything on it runs well, and I think the first owner kept up with maintenance on this car and the last owner treated it like a beater. I changed the plugs when I got it and they looked well worn but the engine looked healthy, along with engine and cabin air filters. A wheel stud was broke off on the front passenger and when I changed that out it had been broke for quite some time, but the brake pads looked good. The oil drain plug was stripped and a universal plug is on it, so I have a new oil pan bottom and some rtv to change that out, and I started to flush the brake fluid but need to finish that too. After that and the O2 sensor I'm hoping to get a bunch of miles out of it, as I have an extra 2500 miles a month that I used to not drive added recently, and all my other cars/truck get way worse fuel economy. I just wanted a cheap car that gets incredible fuel economy, and an old Prius works great. We will probably get another one soon to add to the fleet too.
     
    #4 sandmanx, Jun 24, 2026 at 11:04 PM
(You must log in or sign up to post here.)