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Car Water Temperature Gauge

Discussion in 'Automotive Electronics' started by clive2016, Mar 18, 2017.

  1. clive2016

    clive2016 New Member

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    Hi Guys

    Can anyone help me, the water temperature gauge on my car has stopped working, by that I mean the needle doesn't move off cold even when the engine has reached full operating temperature.

    I've pulled the wiring plug off the engine sensor unit and found two connections inside it and when using a multimeter between these two connections, with the ignition switched on have obtained a reading of 5 volts.

    Ok I know it may well be the sensor itself which is at fault, but how can I check the gauge, my question is can I simply put a jumper lead between the two connectors inside the plug which I pulled off the sensor, turn the ignition on and observe the gauge movement.
    Apart from the needle swinging over to the maximum temperature if its working correctly, will doing this damage the temperature gauge, the last thing I want to do is blow it up.

    Thanks to anyone who can put me straight on this.

    Clive
     
  2. Diver300

    Diver300 Well-Known Member

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    It's not likely that shorting the sensor will do any damage, but it could happen.

    What is the resistance of the sensor? Is there any conductivity to ground?

    Also, 'car' could be just the slightest bit vague here. We know that it's got a temperature gauge, an electrical system, and most likely an internal combustion engine, or there wouldn't be a temperature to measure, but being a bit more specific might mean that you get a better answer.

    Make, model and year of production would be a good start.
     
  3. shortbus=

    shortbus= Well-Known Member

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    Also many cars now days have more than one temp sensor. One for the gauge, usually some where along the side of a cylinder head and another one near the water outlet for the ECM. The one for the ECM is the easiest one to see but has nothing at all to do with the temperature gauge.
     
  4. dave

    Dave New Member

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  5. clive2016

    clive2016 New Member

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    Diver300 and Shortbus=

    First thank you both for your quick replies it’s very much appreciate, I have to say I’m not really into electronics but with your help maybe I can sort the problem.

    Ok the car in question is a Vauxhall Omega 2.5TD year of manufacture 2000, it’s the one with a 6 cylinder BMW engine in it as standard.

    Yes, I can see the two sensors well actually at this very moment they are sat on my computer desk and as you said Shortbus they both live on the same side of the cylinder head, the one nearest to the car radiator only has one connector inside it.

    The one nearest the bulkhead has two and I’m guessing this is the one for the water temp. gauge although I may be wrong, never the less this is the one I’ve tested as follows:

    After holding it under a cold running water tap the resistance measured 3300 ohms and then running hot water on it the resistance was 740 ohms.

    I’m sure I saw on a video clip it should be down to around 275 to 375 ohms so I’m assuming the sensor is shot but having said that I would like to confirm the gauge is ok, if it isn’t it will be a first in all my years of motoring.


    Diver300 sorry to appear a bit dim, you asked if there was any conductivity to ground, I did a continuity check between ground and one of the connectors inside the plug which I pulled off the sensor and the buzzer sounded on my tester and I did get a 5 volt reading between the two connectors inside the plug, if that’s what you mean?


    Thanks again for your help guys

    Clive
     
  6. Diver300

    Diver300 Well-Known Member

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    I was suggesting that you test if the sensor conducts to ground. A sensor with 2 terminals will usually be isolated from the case.

    If the sensor is changing from 3300 Ω to 740 Ω between cold and hot water, it is highly unlikely to be faulty.

    275 Ω to 375 Ω sounds a bit low for a cold resistance, but could be right for a hot resistance. Your sensor could well get down to around those values at normal running temperature.

    As you are getting a voltage at the terminal where the sensor connects, it looks like the gauge is faulty. However, that car is 15 years newer than one that I had where the temperature sensor connected to the engine management computer, and an output of the computer drove the temperature gauge, so you can't assume a direct connection.
     
  7. clive2016

    clive2016 New Member

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    Diver300

    Both sensors have brass threads which screw straight into the engine which I assume grounds them, I’ve got to admit I don’t even know if I’m testing the right sensor ie: the one with two terminals which is nearest to the car bulkhead.

    The 275 - 375Ω is what I’d seen on a video for the hot water test on a Chevy, mine reads 740Ω for the hot water test of course the 740 reading may be perfectly ok for an Omega, I don't know.
    If the gauge works off the sensor with one terminal, do you know how I can check the plug for voltage, is it just a case of connecting the meter between the plug terminal and the engine ground???

    You’ve just ruined my day saying the sensor may connect to the engine management computer and from there to the gauge.
    I can see me having hours of fun trying to sort that out, when I already don’t know what I’m doing, I'm not into reading wiring diagrams and the only Haynes Manual I've got is for the petrol Omega 1999, they never did one the diesel.

    If I can at least check I’m getting voltage at the two sensor plugs, I guess I’ll just have to buy two new sensors and put them in, put everything back together and see if the gauge works then.
    It’s a real pain getting the inlet manifold off on these things and there isn’t a cat in hells chance of getting at the sensors without pulling it off.

    Thanks again

    Clive
     
  8. Diver300

    Diver300 Well-Known Member

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    Sorry that I've been the bearer of bad news.

    Some temperature sensors have just one terminal and the return path is through the screw thread. Temperature sensors with two terminals are likely to be isolated from the screw thread.

    It doesn't look like the problem is the sensors, but they are cheapish and easy to change, so it could well be worth trying.
     
  9. debe

    debe Active Member

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    In most cases the 2 wire sensor is the ECU sensor, especialy if it has 5V on it. The single wire one is most likely the Temp gauge sensor. If you ground the single wire the gauge should go hard over. Also the gauge sensor is usualy near the front of the engine by the thermostat.
     
    Last edited: Mar 18, 2017
  10. debe

    debe Active Member

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    Typical sensors on a car. TEMP.1.JPG TEMP.2.JPG
     
  11. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    If you disconnect the wire from the single-terminal sensor, and substitute a 500Ω pot (wired as a Rehostat), with one end of the pot connected to vehicle ground, you can cause the gauge needle to move across the gauge scale as you turn the pot. If you want to know what resistance corresponds to any given temperature, turn the pot until the needle goes there, and measure the pot with an Ohmmeter. This works for fuel senders, too.
    Most of those sensors have a negative tempco, so the resistance decreases as they get hotter.
     
  12. clive2016

    clive2016 New Member

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    Diver, debe and Mike

    Absolutely brilliant guys, it's dark over here in the UK at the moment, I haven't got a pot but tomorrow I'll see if my Local Maplin Store has one in stock.
    Mike thanks for the holiday snaps :) Will a 500Ω one be good enough for the job?? I can see from Maplin's web site they have shed load of different ones.

    I'm going to sign off for now fellas but I promise, I'll be back on tomorrow and let you know how I get on.

    Thanks once again chaps for your time
     
  13. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Most senders I have played with in cars, boats and airplanes are ~500Ω cold , and ~30Ω hot. The gauge is nothing but an ammeter, where the resistance change of the sender varies the current through the gauge (D'Arsonval meter). In some installations, the upstream end of the meter is fed from a crude voltage regulator that makes ~5V from the car's 12-14V electrical bus (car instrument regulator).
     
  14. clive2016

    clive2016 New Member

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    Hi Guys
    I'm back again, just to recap on what I've done so far, both sensors have been removed from the car, the plug to the sensor nearest the bulkhead has two pins in it, when a voltmeter is connected to them and the ignition is switched on I get a reading of 5 volts.

    The plug which fits onto the sensor nearest to the radiator has one pin in it when a voltmeter is connected to the pin and battery earth and the ignition is switched on I get a reading of 11.9 volts.
    If I then connect a variable 1k Ω potentiometer between the pin in the plug and battery earth and switch the ignition on the water temperature gauge does not move, if I turn the spindle on the potentionmeter and check again the water temperature still does not move.
    I'm assuming the senor with the single pin plug is the one which controls the water gauge, has anyone got any ideas where to go from this point.

    Cheers

    Clive
     
  15. clive2016

    clive2016 New Member

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    P1210433.JPG P1210429.JPG
    Single pin sensor
     
  16. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Presumably, those readings are looking back into the cable connectors, with the connectors unplugged from the sensors, correct?

    What happens if you connect your Ohmmeter between the single pin and the Brass nut on the sensor? Polish an area on the Brass using a ScotBright pad or fine steel wool. Heating the sensor in the palm of your hand might change the reading, probably to a lower resistance?

    The next step would be repeat as above, but immerse the sensor in boiling water.
     
  17. clive2016

    clive2016 New Member

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    Hello again Mike
    I was rather hoping you'd be back on here tonight, I don't know if there is any way of private messaging someone on this forum and it comes up in their e-mails as an alert, I know some forums do.
    Mike yep you are absolutely bang on the readings are looking back into connectors having been unplugged from the sensors.

    I've just picked the sensor up off my desk given the nut a polish, then stuck it under a cold water tap and got a reading of 1.4KΩ and under a hot running water tap a reading of 0.302KΩ
     
  18. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I would guess that the Sensor is working properly. Since the gauge didn't move when you did the pot test, I'm thinking that the problem is in the gauge.

    Let me ask you; back when the gauge was working normally, did the gauge sweep back-and-forth every time you turned on the key? Is so, the gauge is controlled by a micro-computer; it is a stepping motor; it is not just a simple mAmpmeter.

    It might be a DC meter that is controlled by the micro-computer, in which case, there are several areas where the root cause of the problem might be...
     
  19. clive2016

    clive2016 New Member

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    Hello again Mike

    I did a further test by connecting a jump wire directly onto the battery neg and the other end of the wire touched the pin in the plug which pushes onto the sensor, with the ignition switched on the gauge didn't move.
    In answer to your question, no the gauge did not swing back and forth, it was stable when it was working, slowly moving as the engine got hotter.
    You know Mike this is looking very much like you say, the gauge itself is shot.

    I'll have to pull the instrument panel out, I'm not sure if I can test the gauge further once it's out as a final confirmation that it's a trash job.
    I'll get back to you once it's out, taking instrument panels out of cars is a real pain especially when there is no workshop manual to cover it, I know in addition to the screws holding them there are a load of plastic clips which you have to try and spring out, they are normally an integral part of the plastic molding and more often than not break off.

    When I took an instrument panel out in a different car, I ended up having to take the steering wheel off and of course the airbag, I remember I wanted to test something so had to reconnect the battery.
    I switched the ignition on to check whatever it was and never thought any more about it, until everything was back together only to find the airbag warning light would not go out, so ended up having to take the car to a garage so they could use their laptop with appropriate software in order talk to the car and make it go out.
    I was told that even with the airbag out of the car switching the ignition on trigger a fault, so i wont be making that mistake this time.

    While I've got your attention I'd like to ask you about something else, the outside air temperature which is displayed on the in car display has started dancing up and down, I know it could be the outside sensor is there a way of testing them?

    Thanks
    Clive
     
  20. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Depending on how much you love that car, I would be inclined to not screw with the instrument cluster, and just mount one of these somewhere on the dash...
     
  21. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Same problem, without a shop/service manual, you are reverse-engineering an unknown design. The sender is likely a neg-tempco thermistor, but it could be something else...
     

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