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355 Water temp gauge reads from Thermistor or ‘sensor

Discussion in '348/355' started by Cirorsi, Jun 6, 2019.

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  1. Cirorsi

    Cirorsi Formula Junior
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    #1 Cirorsi, Jun 6, 2019
    I need to calibrate my water temp gauge, is the reading from the Thermistor (39) or the sensor (40) on the rear of the manifold? Thanks in advance.

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  2. Ricambi America

    Ricambi America F1 World Champ
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    Dec 7, 2003
    16,443
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    #2 Ricambi America, Jun 6, 2019
    According to my internal notes:

    125769 IS FOR THE IGNITION ECU ONLY AND DRIVES THE OBD ERROR: COOLANT TEMP OUT OF RANGE. ./ 148677 IS FOR THE INSTRUMENT PANEL GAUGE *AND* WARNING LIGHT ON THE DASHBOARD.​

    However, these notes are pretty old on my system, and I'm not 100% sure I ever physically verified these two statements.
     
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  3. Qavion

    Qavion F1 World Champ
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    #3 Qavion, Jun 6, 2019
    Last edited: Jun 6, 2019
    Can you see the wire colours on either of the sensors?

    The gauge sensor wires are grey and grey with a white stripe. The other one has a black with a grey stripe and grey with a black stripe. So if you see any black (other than oil, etc), it's not the one.
    Unfortunately, these engine harnesses tend to be sealed.

    This applies to the 5.2 car. I haven't checked the 2.7 car yet.
     
  4. Cirorsi

    Cirorsi Formula Junior
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    #4 Cirorsi, Jun 6, 2019
    Thanks Daniel and Ian. I’ll take a look at the wiring.
     
  5. Qavion

    Qavion F1 World Champ
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    #5 Qavion, Jun 6, 2019
    If you can see the wire colours, short out the grey-white wire socket on the connector to earth (with the ignition on). This should put on the light.
     
  6. m.stojanovic

    m.stojanovic F1 Rookie
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    #6 m.stojanovic, Jun 6, 2019
    It should be 39, called Transmitter (not Thermistor). It should have a round brass plug on one of the flats of its hex body. Also, one of its pins will give you certain Ohms reading to the ground (NTC resistor); that pin is connected to the temp gauge and the temperature dependent resistance of the NTC drives the gauge needle.
     
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  7. Qavion

    Qavion F1 World Champ
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    #7 Qavion, Jun 6, 2019
    I confirmed Daniel's notes by checking the Workshop Manual (page B78). Item #40 in the catalogue is the one which talks to the ECU (i.e. the rear one). You need the other one #39 (P/N 148677).

    I've added these part numbers to my wiring diagrams (see component number 04720):

    F355 5.2 Instrument Wiring Diagram

    I don't know the socket orientation on the plug, however.

    5.2 Engine Management System Wiring Diagram
     
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  8. taz355

    taz355 F1 Veteran
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    #8 taz355, Jun 6, 2019
    Mine is from 39 on your diagram for sure because i jad to fix it once. Its a 99F1
     
  9. Qavion

    Qavion F1 World Champ
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    #9 Qavion, Jun 7, 2019
    For info: I just had a look at my gauge sensor harness connector. Looking at the connector with the clip on top, if I short the right socket to earth, it puts on the light (with the ignition on). I updated my diagram (just click on the previous link and refresh your browser as required)

    Slightly off topic, but as always, when I start looking into these things, I find something else broken on my car :rolleyes: The coolant cap appears to be leaking from the top. Fortunately, they are not expensive, thanks to Joel on FChat:

    https://www.ferrarichat.com/forum/threads/coolant-caps-mta-rated-1-0.556226
     

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