Water temp sensor fault

Discussion in 'GENERAL R DISCUSSION' started by Danroyd, Jul 27, 2017.

  1. Danroyd

    Danroyd Member

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    I got a consult cable to see why my car fans weren't switching on when the car got hot and i can see now its tripping out it gos from 80degrees to 0 then back up continuously, its a new sensor , ive checked the continuity on the 2 wires back to the ecu and there good so now in stumped has anyone got any idea's? How do the ground wires going to the ecu work?
     
  2. Mr B

    Mr B Member

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    Have you checked the 5v reference signal at sensor harness to the sensor is correct
    have you check earth continuity from sensor harness to engine ground
    Have you checked/cleaned ecu harness plug/pins, sensor harness plug/pins
    Have you pulled sensor out and tested it in heating water with multimeter on sensor, just because it new sensor doesn't mean it good sensor (aftermarket sensor quality can be awful)
    What values ecu get with sensor disconnected and disconnected with pins bridged (fans should run bridged)
    Also have you checked fan operation either by switching fans via diag software or manually by grounding pin 9 on ecu .
    FSM sensor info in link below:
    https://drive.google.com/file/d/0B7Ub2apq5-pfMDRwZHhuRktnLVk/view
     
  3. keastygtir

    keastygtir Well-Known Member

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    What he said!
     
  4. Danroyd

    Danroyd Member

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    Im getting 4.9v from the sensor wire
    Continuity on the earth is 12ohms back to the battery is that to much?
    And the heat gauge on the computer starts at like 30 and slowly increases to 80 with the sensor harness disconected.
     
  5. Mr B

    Mr B Member

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    reference voltage seems good .
    earth has continuity but not sure what average resistance value is with ign key off so 12ohm could be classed as suspect at moment.
    I would assume the 30 to 80 sensor disconnected slow temp increase is ecu limp mode value for water temp, does it stay at 80 once reaches it ? (if is constantly cycling 30 to 80 disconnected would assume earthing/circuit issue)
    What happens to temp value if bridge the pins in sensor harness and do fans kick on (if fans not known working test circuit by grounding pin 9 via a back probe, 100ohm resistor good way bridging/testing.
    Have you done a basic test of the coolant sensor resistance at room temp and in water being heated, if value flickering or way off FSM spec then that the fault. if Sensor tests A1 with no doubt then it earth wiring related by looks of things, if you got issues with more sensors etc it could all be related to same poor earthing perhaps .
    Doing all tests above and reviewing date should eliminate more areas and give direction to what at fault or how test it further .
     
  6. Danroyd

    Danroyd Member

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    Yip with it disconected it raises to 80 and stays on 80, with the two wires bridged the fans come on thats how im running it atm, yea i had same issue with the old temp sensor but ill test the new one anyway, so where does the ecu get the earth from? Am i best to try re-earth the ecu or just earth the sensor sttaight off the engine next to the sensor?
     
  7. Mr B

    Mr B Member

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    ECU has a couple of main grounds (pin 6 & 13) but if had main ground issues at ecu would expect lot of issues not just ECT sensor.
    Worth checking grounds though just be sure .
    You can't just re-earth the sensor as the earth return at pin 21 is the analogue data input for the ecu (ecu is reading voltage difference in what is basically a potential divider circuit and pin 21 is the tap off point for that measurement)
    If ECT sensor test fine which likely will if you on second sensor yet same issue persists, this would make the ECT return wiring suspect to pin 21 & 29 (29 is shared earth with tps switch, does tps function properly/test to FSM spec ?, if disconnect tps any difference to ECT reading ?)
    You could run through this wiring and connector points or do a quick test with resistors or ECT sensor wired direct to ecu pins 18 21 & 29 via back probes and see if ecu can actually read a good signal via displaying a realistic temp to resistance you implementing in the circuit, if so you know wiring bad and can dig into it further, if still doing much same it could be ecu circuit gone bad.
    My hunch mainly as most common will be towards wiring but it wouldn't be first time I heard/seen ecu fault on ECT circuit .
     
  8. Danroyd

    Danroyd Member

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    Ok ill check the wiring and all the earths of the ecu and see if thats the problem , thank you for your help il get back to you on what i find
     
  9. Danroyd

    Danroyd Member

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    Ok so i checked continuity on the earths and they seem good , and i went a brought a new oem nissan coolant sensor and its reading fine gets up to 80degrees but the computers not switching the fan on? It switches on at 80 right?
     
  10. Mr B

    Mr B Member

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    fan switching around 100 . either wait for fans cut in/out with car running (take while and get hotter than you think) or test circuitry by simulating 100deg+ with a resistor bridging sensor connector, variable resistor pots can be had for £2 and few of them along with some standard resistors make excellent diagnostic aid for car sensors and circuitry .
     
  11. Danroyd

    Danroyd Member

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    Oh really , at 80c my gauge was nearly up at the line , do you know wat resistor represents 100?
     
  12. Mr B

    Mr B Member

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    200ohm to low 100ohm , variable resistor more usable tool but basic resistors will do job .
     
  13. Danroyd

    Danroyd Member

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    Ok ill give that a go thanks
     
  14. Danroyd

    Danroyd Member

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    Ok i put a 180 in and it read 101 degrees on my computer and the fans were on , so i was just going to let it get to that on the computer but on my gauge it looked like it was overheating at 85 degrees so i dont know what to do could my gauge be playing up? 20170811_180657.jpg
     
  15. Mr B

    Mr B Member

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    Gauge or sender for gauge out of tolerance I would assume, test sender or buy quality new one (lot of R's get wrong/cheap senders fitted so always keep that in mind), as it ntc sender you could calibrate it to some extent by putting a resistor inline on the single wire. they read about half for normal running and little over to almost 3/4 max for normal hot and fans just switching on then fall back to around half .
     
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  16. Fast Guy

    Fast Guy Moderator Staff Member

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    I think the fans come on at 94 or 95ish.
     
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  17. Danroyd

    Danroyd Member

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    Ok i will get a new oem one from nissan and try that
     
  18. Mr B

    Mr B Member

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    To be totally exact it has variations based on vehicle speed.
    below 20mph fans switched on @ 100degC
    above 20mph and to 80mph fans switched on @ 96degC
    above 80mph fans switched on @ 105degC

    * values above based on aircon "off"
    * for stationary testing ecu fan ground switching circuit _ simulate 100degC+ 105degC+ input values
     

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