Showered my engine bay with coolant, now Check Hybrid triangle

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by stokesey, Jul 22, 2026.

  1. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    First sign of trouble was water pump laboring. I thought it was going out. Was on dirt road at 10,000ft so I let her cool down and then tried to limp down the hill, mostly coasting. Then realized pump was OK and I was just losing coolant. Drove up on a rock and saw coolant running out on the driver's side of the engine bay. Noticed that an EGR cooler hose had burst. Repaired the hose and refilled with water, drove OK at low speed for 10mi back into town. No temp light again. Then the dreaded check hybrid system light came. Disabled throttle pedal and would not let me drive. I tried my best to find areas that got wet with hot coolant. Surely the connectors under the EGR are all suspect.

    I can idle now and charge the hybrid battery. After 5-10 minutes at idle, check hybrid comes on again. No obvious fault and I don't have Techstream with me. A handful of codes for engine temp cleared and didn't come back.

    Current situation is she's drying out and I have hybrid and start battery unplugged. I'm hoping the fault goes away after everything dries up.

    Any thoughts? Thanks
     
    #1 stokesey, Jul 22, 2026
  2. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    I disconnected the hybrid and start batteries to reset the hybrid system. Error keeps coming back. Although it seems to take longer to throw the error now.
     
    #2 stokesey, Jul 22, 2026
  3. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    11,086
    6,950
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    You really need codes.

    What kind of code reader do you have? A bluetooth app?

    Somebody reported O'Reillys Auto Parts had a hybrid capable scanner for customer scans.
     
    #3 rjparker, Jul 22, 2026
  4. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    P261B Engine Coolant Pump B Control Malfunction

    came back, also

    P0117 Engine Coolant Temperature Sensor 1 circuit low

    Looks like an issue w pump and/or temp sensor
     
    #4 stokesey, Jul 22, 2026
  5. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    28,717
    19,016
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    P261B is the code for the water pump doing less than 900 RPM when it should be doing well above that. So your first feeling that the water pump was "laboring" probably was accurate, and you shouldn't have been so quick to have "realized pump was OK".

    P0117's fortune cookie sounds innocuous enough: the coolant temperature sensor circuit is low, how bad can that be, right?

    Except the Prius uses negative-temperature-coefficient thermistors. Their resistance goes lower the hotter they get. When it gets low enough to set P0117, that means the reading is so hot the ECM isn't even sure if it's a real reading or not.

    But with you knowing your water pump isn't working, that's very probably a real reading that you should take seriously. Get the pump fixed and don't keep overheating the engine so much. That's probably what sprayed the engine compartment and what burst the hose.

    There is a safety rule programmed into the ECM, such that when it has a known water pump code like P261B active, it makes its own effort not to let the engine overheat like that. With a water pump code present. if the coolant hits 105 ℃—which is lower than the threshold for overheat warning lights, so you won't even have seen a warning yet—it just shuts the engine right off, without even telling the power management control ECU why. The power management control ECU then sets its own P0A0F code—"hey, how come the engine's not running?"—and lights the triangle light. Of course your go pedal isn't going to get you much of anywhere then, 'cause there's no engine to do the work, and the battery all on its own is barely capable of rolling you a block or two down a city street.

    But if the water pump is bogging down intermittently, the ECM might be getting fooled into letting the temperature climb above that limit. That particular 105 ℃ limit is only enforced when a water pump trouble code is current, so if the code goes away (or is cleared) and hasn't been set again yet, that limit's not enforced.
     
    #5 ChapmanF, Jul 22, 2026
    Brian1954 likes this.
  6. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    11,086
    6,950
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Sounds like it is overheating with a water pump and high temperature (too high) code. It would useful to read the engine coolant temperature with the undisclosed scanner.

    Water pump flow should be visible in the reservoir when warmed up.
    gen3 coolant reservoir flow w arrow.jpeg

    The temperature sensor code by itself could be air in the system or a wet connector. Might try a hair dryer on the connector near the radiator hose attached to the engine.

    Location of Engine block coolant temp.jpeg
     
    #6 rjparker, Jul 22, 2026
  7. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    28,717
    19,016
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Or just use the undisclosed scanner to view the temp sensor reading. If it's something close to the right temperature you expect when the engine has been off and cooled to the temperature of the surroundings, then you don't have to spend much time on the possibility it's a wiring or connection issue. It is probably also right when the engine is running and it's saying the unpumped coolant is too hot.
     
    #7 ChapmanF, Jul 23, 2026
  8. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    Holy sh*t I was wondering why I didn't get a temp warning light. Also the Check Hybrid System warning is a huge red herring, but I see that others have this when the pump goes. Funny because I verified the pump was spinning but didn't consider it's probably not spinning fast enough. Scan tool didn't allow me to read that PID. Final death knell for the pump was probably running on creek water with no coolant for 10 miles:eek:.

    O'Really wants SIX HUNDRED for the Chinesium pump so I overnighted an Amazon unit for $100 which has "steel impeller upgrade". Also have another pump from an engine I rebuilt so maybe I'll tear into the pump and see if it can be rebuilt.

    I drove the car super easy for less than 20 mi so hopefully not too much damage. And I rested it every 3 or 4 miles.
     
    #8 stokesey, Jul 23, 2026
  9. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    Good call, there was definitely some air in the system. Nice technique with the light on the coolant tank.

    Its basic Chinese ELM327, ECU reported around 180-220°F but I don't believe it. Definitely saw flow in the coolant reservoir but probably insufficient.
     
    #9 stokesey, Jul 23, 2026
  10. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    11,086
    6,950
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Its good to know normal coolant temperature behavior on a gen3 which requires some reading or proactive monitoring. 220f is about 25f too hot. Might reach 205f under an extremely steep backroad hill climb returning to normal in about a minute.

    App is still undisclosed. Car Scanner can read both temperature sensors as can Techstream.
     
    #10 rjparker, Jul 23, 2026
    Last edited: Jul 23, 2026
  11. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    Yep, Car Scanner for the win. Water pump went in easy from the topside, did one bolt on bottom blind. Slowly seeped coolant away from AC compressor into the under cover and caught every drop.
     
    #11 stokesey, Jul 23, 2026
  12. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    Temp sensor code went away, maybe the connector dried out? Coolant temps between 180 and 199°F on an hour drive in 98°F heat with AC on full. No other warnings or codes so I'm calling this fixed.

    Truth be told the behavior of this car's electronics is odd when the water pump is on the way out, but its incredibly easy to fix once you understand the system. Toyota engineering for the win.

    Thanks to all for the informative replies. I had one shot to fix this as I am out in the wilderness and the nearest parts store was 85mi away. I had no tools so I bought a cheapo metric socket set and was able to get the job done in 90mins. Whew!
     
    #12 stokesey, Jul 23, 2026
  13. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    Oh and BTW my pump is seized up solid. Impeller won't even move. Will see if the root cause is the usual rotor deformation and report back. Hearing good things about the steel rotor upgrade.
     
    #13 stokesey, Jul 23, 2026
    Mendel Leisk and Brian1954 like this.
  14. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    11,086
    6,950
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    I have one of these stored in the hatch

    IMG_2220.jpeg

    I would probably buy a new oem pump from an online Toyota dealer but if I were caught at 10,000 ft.,,
     
    #14 rjparker, Jul 23, 2026
    stokesey and Mendel Leisk like this.
  15. stokesey

    stokesey Junior Member

    Joined:
    Oct 19, 2024
    93
    14
    0
    Location:
    Southern Cal
    Vehicle:
    2015 Prius
    Model:
    Two
    The rotor seems to be the failure point. I got an Amazon pump with a metal rotor, claim is that the metal one is more durable? Metal rotors are cheap too. The Autozone $500 pump has the plastic rotor.

    Scan tool reporting 3075rpm pump speed when commanded speed is 2425rpm. And its spinning at 4000rpm when commanded at 3000rpm.

    [​IMG]

    Any why am I diagnosing the pump so extensively would might ask?

    Because I've changed my pump out twice now, and I'm getting the dreaded P0AA6. Was hoping it was just the 12V battery but its looking like I might've fried my AC compressor with some coolant spillage? Dangit. I haven't gotten the subcode yet but unplugging the AC compressor high voltage line makes the code go away... Oh boy
     
    #15 stokesey, Jul 28, 2026
(You must log in or sign up to post here.)