P0118 after head gasket replacement and full engine coolant change

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by anonymous, Nov 19, 2019.

  1. anonymous

    anonymous Member

    Joined:
    May 18, 2015
    113
    71
    0
    Location:
    California
    Vehicle:
    2011 Prius
    Model:
    II
    After changing the head gasket and changing all the engine coolant in the process, now I'm stuck with a P0118 "Engine Coolant Temperature Sensor 1 Circuit High". The sensor is plugged in of course but it always immediately returns when clearing codes. I sprayed some brake cleaner into its connectors and they look fine. Freeze frame shows sensor reports -40 degrees.

    But the thing is, when I unplug the sensor, the red temperature light illumates on the dash. If the circuit is open then how would it be any different than when it's unplugged?

    Do you think the sensor is bad? How could the sensor just go bad like that?
     
  2. anonymous

    anonymous Member

    Joined:
    May 18, 2015
    113
    71
    0
    Location:
    California
    Vehicle:
    2011 Prius
    Model:
    II
    I tried shorting the pins for the sensor but didn't get P0117 :confused:
     
  3. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

    Joined:
    Oct 17, 2010
    37,669
    26,471
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Here's a test procedure for it:
     
    Robert Holt and SFO like this.
  4. anonymous

    anonymous Member

    Joined:
    May 18, 2015
    113
    71
    0
    Location:
    California
    Vehicle:
    2011 Prius
    Model:
    II
    Thanks; I also found this manual which is more relevant:
    https://attachments.priuschat.com/attachment-files/2018/04/144922_P0115P0117P0118.pdf

    This is a bizarre issue :confused:
    I used an alligator clip to connect the pins together on the harness end; theoretically this should trigger a P0117, but it doesn't. (IIRC last time I shorted the pins, clearing the codes immediately threw P0118 again.) Temperature light illuminates with this short circuit or with a complete open circuit, but does not illuminate when the sensor is plugged in.

    Using the manual I tried checking for continuity from the ECM connector, but I cannot seem to get any continuity between THW/THW and ETHW/E2. The only thing I get is ~1450kOhms between ETHW and either pin on the sensor connector, but that probably means nothing. :confused:
     
    Mendel Leisk likes this.
  5. anonymous

    anonymous Member

    Joined:
    May 18, 2015
    113
    71
    0
    Location:
    California
    Vehicle:
    2011 Prius
    Model:
    II
    IMG_7931.jpg

    facepalm.png

    (There is another coolant temperature sensor in the head that I forgot to plug in. :rolleyes: (I was looking at the one on the coolant hose))
     
  6. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

    Joined:
    Oct 17, 2010
    37,669
    26,471
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Ah, the little white connector? I didn't peek at the spoiler.m

    Still haven't.
     
  7. anonymous

    anonymous Member

    Joined:
    May 18, 2015
    113
    71
    0
    Location:
    California
    Vehicle:
    2011 Prius
    Model:
    II
    Yeah, open the spoiler; I thought it was the temperature sensor on the coolant hose above the EGR cooler that was causing the problem, but actually it's the temperature sensor in the engine head that I completely forgot about.
     
    Mendel Leisk likes this.
Loading...