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Thread: How to test coolant sensor loom for 5v?

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  1. Re: How to test coolant sensor loom for 5v? 
    #11
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    "
    With the ECU unplugged there is no continuity between the terminals in the the G62 sensor loom plug. "

    That is what you would expect to see, but you should also test on a high ohms range from each pin at the G62 plug to battery negative or chassis, just in case one of the wires is in contact with a different circuit.
    This test should also be clear.

    "
    With the ECU plugged back in, there is continuity between the terminals in the the G62 sensor loom plug."

    There are components within the ECU that will give a resistance reading, what is the resistance you are getting ? ( be carefull which ohms meter range you are on, the wrong range can give misleading results )
    As stated previously, a short would be less than 10 ohms, but a much higher resistance would probably just be the components accross the circuit within the ECU.

    "
    there is continuity between the red/grey sensor terminal and the Ecu pin 52 in Ecu loom connector.

    - there is continuity between the brown/grey sensor terminal and the Ecu pin 53 in Ecu loom connector. "

    I don't have access to your wiring diagram, but I am presuming those are the wire colours at the G62 Plug as well.

     
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  2. Re: How to test coolant sensor loom for 5v? 
    #12
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    "With the ECU unplugged there is no continuity between the terminals in the the G62 sensor loom plug. "
    That is what you would expect to see, but you should also test on a high ohms range from each pin at the G62 plug to battery negative or chassis, just in case one of the wires is in contact with a different circuit.
    This test should also be clear."


    I have already tried the continuity test from both the G62 loom connector pins to the chassis / engine earth bolts / gear box earth bolt and it beeps and they have continuity. This is with the Ecu plugged in. I didn't note the exact resistance ohms reading though. Are you asking me to check the exact value and that might help us determine something? What ohms range do you want me to try it on?
     
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  3. Re: How to test coolant sensor loom for 5v? 
    #13
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    What I am saying is, with the ECU un-plugged, with your meter set to its highest ohms range, attach one meter lead to battery negative & the other lead to each of the two pins at the G62 plug in turn.
    The meter should show infinity in both cases.

    If it doesn't, it will show there is some contact with another circuit which there shouldn't be.

    If it shows infinity, & with your other tests you have done, there doesn't appear to be a problem with the circuit for the G62 sensor.

    You really need to plug into VCDS & see what that is reporting for the G62 & anything else.
     
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  4. Re: How to test coolant sensor loom for 5v? 
    #14
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    Ok, I'm only getting back to this now.

    I checked the G62 reading via VCDS whilst driving with it connected, when I first started driving the gauge was all erratic and the VCDS value was also erratic, then the gauge settled at 90 and VCDS settled too, so VCDS value seemed to replicated what the gauge was displaying. When gauge settled at 90 VCDS value was settled at 85.5 degrees.

    I bought a 2nd hand loom and planned to swap it over after testing it, I didn't test it yet. However, another twist,,, the continuity I had at the G62 sensor plug terminals isn't there now. I left my multimeter probes in the sensor plug and wiggled the bunch of cables at the Ecu and continuity didn't occur/beep.

    Something else changed too, the voltage readings at the G62 terminals when the ignition is switched on, I now get:

    Probe on Neg battery post and probe on Red and Grey G62 cable = 3.35v (Used to be 0.04v)
    Probe on Pos battery post and probe on Red and Grey G62 cable = 8.44v (used to be 11.74v)

    Probe on Neg battery post and probe on Brown and Grey G62 cable = 0.04v (Same as before)
    Probe on Pos battery post and probe on Brown and Grey G62 cable = 11.78v (same as before)

    My battery voltage read 12.46v
    With the ignition key off I get 0v on both G62 terminals when on Neg battery post and 12.40v when using Positive post.

    So, anyone got any idea why the situation has changed,,,, mainly why the continuity has disappeared at the G62 plug and why I now have 3.35v on the Red+Grey cable at the G62 plug when it used to be 0.04v and 8.44v when it used to be 11.74v????

    I'm not sure what to do now, do I go ahead and swap the looms now anyway or are the new test readings pointing me in another direction?
     
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