P0117 with Normal temp 180 to 195 F

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by johnnychimpo, Mar 31, 2021.

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  1. johnnychimpo

    johnnychimpo Member

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    Im getting P0117 I have monitored the engine temp it is normal stays within 180 to 195 F so not overheating.
    there is a sensor above the EGR and one below how do you know which sensor has the issue? a but of background I just swapped the engine and put in a Gen 4 engine in this 2010 prius everything runs fine except this code.
    Any suggestions on how to figure out which sensor it is? As Im getting normal temp reading via ODB II phone app
     
  2. ChapmanF

    ChapmanF Senior Member

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    Could there be an intermittent short there? The ECM just needs to see the voltage pulled too far down for ½ second or longer to set that code.

    Not sure about the multiple-sensors story on the transplanted engine, but the one the ECM is talking about should be whichever one you plugged into the brown-and-pink-wired connector D6.
     
  3. johnnychimpo

    johnnychimpo Member

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    above EGR and below EGR. it is my understanding the one above is for your dashboard light both the same just not sure which is the bad one.

    upload_2021-3-31_9-31-23.png

    upload_2021-3-31_9-34-11.png
     
  4. ChapmanF

    ChapmanF Senior Member

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    Did you read what I wrote about how to tell?
     
  5. johnnychimpo

    johnnychimpo Member

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    Yup will check it when I get home.
     
  6. johnnychimpo

    johnnychimpo Member

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    Found the issue. seems the EGR rubbed up on the connector and shorted the sensor replaced and grinded down EGR
    Issue is solved. But I sonder how the computer gets the temp for the engine there being two sensors, Does it give and average based on the two readings?
     
  7. ChapmanF

    ChapmanF Senior Member

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    Judging from the repair manual excerpts that RRxing just posted in this other thread, one sensor may just be wired directly to the combination meter in the dash, to control an overheat light there.
     
  8. johnnychimpo

    johnnychimpo Member

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    Interesting I did unplug the upper sensor and stopped getting readings all together. The sensor by the EGR being bad leads me to believe it is the primary and the one above the cooler is a backup. I suspect this because my reading normally were at 190 to 195 and then when I got the code for the sensor below the EGR readings dropped to 180 185 since the sensor above the EFR cooler is farther away and passed the EGR cooler has more time for coolant to cool. All speculation on my part.
     
  9. ChapmanF

    ChapmanF Senior Member

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    The wiring diagram shows the one connected to the ECM having brown and pink wires, and the one connected to the combination meter having black and white.

    On the other hand, the wiring diagram calls the latter an "oil" temperature sensor. I don't think there is one of those. Oops.
     
  10. johnnychimpo

    johnnychimpo Member

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    Let me get this right do the two sensor work together? I ask because when I disconnect the top one I get overheat light on dash and stop getting readings on the ODB. I figured top is only for the light. And the bottom for temp reading. So disconnecting top sensor will turn on overheat but I should still get a temp reading for the Bottom one right? Oh one more thing do the sensors have fuses?
     
  11. ChapmanF

    ChapmanF Senior Member

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    It would be super helpful for you to include the wire colors connecting to the sensors you talk about, because the wiring diagrams don't always include "this one is the top one" or "this one is the bottom one".

    [​IMG]

    [​IMG]

    When you are reading coolant temperature over the On Board Diagnostics port, what are you using to read it? Does it show which ECU and PID it is getting the reading from?
     
  12. johnnychimpo

    johnnychimpo Member

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    I have not been reading with a phone app and a blue tooth device sorry for the confusion. I will connect the tech stream in the morning see what I can see.
     
  13. ChapmanF

    ChapmanF Senior Member

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    That will probably shed some light.
     
  14. ChapmanF

    ChapmanF Senior Member

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    The OP did find out that there are two different coolant temperature readings and both of them can be read over OBD, one at $7C0 and one at $7C4.

    [​IMG]

    Using Techstream, you can read one of them in the Data List for "Engine and ECT", and the other one in the Data List for "Combination Meter". (I'm not sure how to match those to the hexadecimal addresses shown in the phone app, which Techstream doesn't show.)

    The one that connects to the combination meter is the one that lives in the funky tee fitting in a coolant hose back under the cowl (the same fitting with the coolant bleed valve, for the model years that have that).

    G2.png

    That connector (G2) has a black wire and a white wire. The hose where that sensor is mounted is a weird place, the return hose from the exhaust heat recirculation system.

    ehrs.png

    The sensor that is wired directly to the ECM is mounted right on the cylinder head of the engine.

    D6.png

    That connector, D6, has a brown wire and a pink wire.

    The combination meter does have a red "thermometer" light, which will turn on if the sensor connected to the combination meter (G2, the black/white wired one, in the hose) hits about 248 ℉ (120 ℃).

    248.jpg

    (All the other lights are on there because the engine wasn't really running for that; I just had the car in ON and a potentiometer wired in place of that sensor, so I could twist it until the light came on and see what temperature that reads as. The potentiometer ended up about 106 Ω at that point.)

    pot.jpg

    The specs in the manual don't show beyond 100 ℃, but that resistance seems in the ballpark if you extrapolate.

    It's a little odd that this overheat warning light comes from the sensor in the EHRS hose. Seems a long way for the coolant from the engine to have to travel to tell you it's too hot.
     
  15. ChapmanF

    ChapmanF Senior Member

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    I forgot to attach that image:

    ntc.png

    There is such a section in the manual for each sensor; they appear to have the same specs.
     
  16. mr_guy_mann

    mr_guy_mann Active Member

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    Might be "belt and suspenders" approach to coolant temperature monitoring? The main ECT sensor to the ECM will usually log codes (or trigger ICE shutdown) if that shows too hot. This second one could be backup for overheat indication, and probably is also used to monitor function of the coolant preheat valve on the catalyst.

    Posted via the PriusChat mobile app.
     
  17. ChapmanF

    ChapmanF Senior Member

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    That's what I would like to know. We do know that the main ECT sensor to the ECM will trigger an engine shutdown at 105 ℃ if the ECM is already reporting a problem with the water pump, but when that happens, the driver doesn't get a clear indication that temperature is the reason. The only code in the ECM will be the one about the water pump, and the only code in the power management control ECU will be for the engine refusing to start.

    We also know that the main ECT sensor to the ECM does not trigger an engine shutdown at 105 ℃, or indeed up to 107 ℃, if the ECM is not already reporting a problem with the water pump. Will it shut down at some higher temperature than 107 ℃? I don't know, that's just where I chickened out. Will it give the driver any visible indication of an overheat? It would be nice to know.

    The ECM will log a P0117 if that main ECT resistance gets so low it looks shorted. But that would correspond to a coolant temperature above 284 ℉ (140 ℃). You would probably want to get an overheat indication somewhere below that. A reading that high would look more like a sensor problem (we hope!), which is what P0117's fortune cookie would suggest.

    Can somebody check what the ECM actually does with high temperature values from the main ECT sensor? The same technique I used above, spoofing with a potentiometer, can be used; according to the manual, both sensors have the same temperature-to-resistance curve. I can't keep filling every weekend with PriusChat experiments.
     
  18. johnnychimpo

    johnnychimpo Member

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    Yup now thinking about it my engine shutting down was due to my water pump performing poorly then dying. At the time I had just unplugged my EGR to trouble shoot misfire issue so my conclusion was the computer did not like that. I cleared codes plugged egr back in. Drove home from there short drive 5 min.
    Next morning driving to work got a code for pump failure. Never a overheating light on the dash and I know the dash light works. I tested it. there is a ten degree difference between the sensor above the EGR and the one bellow it next to the engine block. So by the time the car starts to overheat and shuts down you never see the overheat light come on at least I did not.
     
  19. ChapmanF

    ChapmanF Senior Member

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    The other day when I was testing, the difference between the two sensors was a handful of degrees during warmup but eventually narrowed to essentially rounding error, which is kind of what you'd expect when the engine is up to temp and it's pretty much the same coolant flowing past both sensors.

    It's different if the water pump's busted, because then the coolant isn't flowing.

    But if the ECM knows the water pump's busted, it also shuts the engine down at 105 ℃, and that's well below the 120 ℃ where the red-thermometer light comes on.
     
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  20. ChapmanF

    ChapmanF Senior Member

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    I hadn't spotted this before, but the repair manual does say that the red-thermometer light can be triggered by either the direct connection from the sensor in the EHRS hose, or a CAN bus message from the ECM based on the other sensor.

    or.png

    What I would still like to know is what temperature has to be hit, at the cylinder head sensor, for the ECM to send that message to light the light (and does the ECM do anything else at that temperature, or just send the message to light the light?).

    It could be learned by switching in a potentiometer for the sensor, same as I did above but for the other sensor, and seeing what indicated temperature would provoke the ECM into sending that message to light the light.
     
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