Oil Cooler (radiator) fan running constantly | FerrariChat
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Oil Cooler (radiator) fan running constantly

Discussion in '456/550/575' started by usrjd, Jul 21, 2025 at 4:38 AM.

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  1. usrjd

    usrjd Rookie

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    #1 usrjd, Jul 21, 2025 at 4:38 AM
    Hi Guys,
    My recently purchased 456GTA Modificata has given me another problem to solve - the oil cooler fan is running as soon as the ignition is switched on.
    I've checked the Thermistor resistance (the one in the oil tank) when cold and it's showing open circuit, so I 'think' that this is the problem - but can anyone tell me the cold resistance reading for a known good one...?
    Any info would be muuch appreciated before I spring for a new one.
    Cheers from Australia,
    Richard
     
  2. Qavion

    Qavion F1 World Champ
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    #2 Qavion, Jul 21, 2025 at 9:51 AM
    Last edited: Jul 21, 2025 at 10:05 AM
    The oil temperature sensor is not for fan control, Richard. It's for temperature display and temperature warning. How are you measuring the resistance?

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    For the temperature readout, you have to go between the brown wire (not the brown/white) and earth, not across both pins.


    The control of the LH/oil fan is via the engine coolant temperature (NTC) sensor in the engine V. See item 33 for the NTC sensor:

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    The RH Motronic ECU receives a signal from the NTC sensor and sends it to the HVAC/DIAVIA ECU. The DIAVIA ECU then activates the LH /Oil Fan relay "I". Or so it does according to the diagram in the WSM....
    I assume (7) is footwell relay "I".

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    I'm still trying to figure out what (5) is. I thought only the 550 had an emergency relay, but it may be one of the relays mounted on the evaporator (see 18)

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    (ignore the red circle).


    I don't know how hard it is to access the NTC sensor to do resistance checks on that, but the resistance should vary according to this temperature chart:

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    If not accessible, you can always take a resistance reading at the RH Motronic ECU
     
  3. Aerosurfer

    Aerosurfer Formula 3
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    #3 Aerosurfer, Jul 21, 2025 at 10:22 AM
    Before you do anything else have you opened up the fuseboard to make sure it hasn't been wired hot to run? Or swap the 2 oil fan relays to see if the problem moves to the other fan? Have you inspected the fuse/relay board overall for the health of the plugs too?
     
  4. Qavion

    Qavion F1 World Champ
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    #4 Qavion, Jul 21, 2025 at 5:00 PM
    I doubt the relays and relay panel plugs would cause the fan to run continuously, but the hotwire is a possibility. Pull relay “I” to see if the fan stops.
     
  5. usrjd

    usrjd Rookie

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    #5 usrjd, Jul 21, 2025 at 11:53 PM
    Hi Guys,
    Thank you for all of the very helpful information - it's very much appreciated.
    To answer Qavion first, I had been checking across the pins,so no wonder it read as open circuit (duh!).
    And I naively expected that the fan sensor would be monitoring the oil temp in the tank and not the water temp....
    Of course, it seems that to replace the sensors. the intake manifold needs to come off, turning a 10 minute job into a potential nightmare.
    And thanks also to Aerosurfer for the tip to see if the fan has been hotwired. I had not known that hotwiring was a 'thing'.
    I'll be able to get back to the car tomorrow to investigate further.
    Cheers to you for your help.
    Richard
     
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  6. usrjd

    usrjd Rookie

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    #6 usrjd, Jul 24, 2025 at 5:42 AM
    The story so far... Both fan relays swopped over, all of the pins look perfect - but no change to the fault.
    So, the relays both check out OK.
    And to check the resistance of the water temp sensor under the intake manifold, I'm now trying to figure out if, (on a Right Hand Drive car) the water temp sensor connects to the RHS ecu, or if it connects to the LHS ecu.
    The Ferrari wiring diagram that I have is not the most intuitive for RHD. o_O
    More to follow...
     
  7. Qavion

    Qavion F1 World Champ
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    #7 Qavion, Jul 24, 2025 at 8:19 AM
    Did you pull the relay to see if the fan stopped as I suggested?


    Everything aft of the centre console should be the same on a RH/LH drive car. The RH ECU reads the sensor.

    What diagrams are you using? There are some serious errors in the original Ferrari diagrams.

    Use this diagram for relay control (see 9A... the fan) and follow the wire to the relay:

    https://www.dropbox.com/t/6zHrR0NRc5TUV1uT

    Here's a diagram showing the sensor:
    (see right hand side)
    https://www.dropbox.com/t/MeRJw9olfCWFEUeb

    Then it's just a matter of figuring out how the data gets to the HVAC system. Maybe the orange/white wire on pin 2 of plug 16D/4L ???
     
  8. usrjd

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    #8 usrjd, Jul 25, 2025 at 12:03 AM
    Hi Ian,
    Many thanks for the wiring diagrams - they are far more logical than the original Ferrari workshop manual ones that I have! Having a properly laid out diagram with colour codes is a huge help.
    Apologies for forgetting to mention, but I did pull the relay when I swopped them over and the fan didn't run, so it hasn't been hotwired.
    It's looking more and more like the temp sensor, but now that I have your diagrams, I can check the resistance at the ecu as a further diagnostic test.
    Can I ask where you found those diagrams as I'd really like to obtain a set?
    Cheers
    Richard
     
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  9. Qavion

    Qavion F1 World Champ
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    #9 Qavion, Jul 25, 2025 at 12:56 AM
    I made them myself.

    I usually don't like to give them out in a package. I am always improving them. Best to ask when you need one... so you have the latest.

    Cheers
     
  10. Qavion

    Qavion F1 World Champ
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    #10 Qavion, Jul 25, 2025 at 2:16 AM
    If your engine is running normally, I'd be surprised if your coolant temp sensor is bad, but I guess we have to do basic faultfinding.

    It should be possible to break up the control circuit into chunks.

    Motronic ECU to HVAC ECU
    HVAC ECU to relay panel.

    How hard is the HVAC ECU to get to (in the passenger footwell on you RHD car)

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    The problem is, I don't know if the Motronic ECU is talking to the HVAC ECU on a serial line, rather than sending a voltage or earth. You might not be able to turn on the fan by putting, say, a ground on a pin at the Motronic ECU connector.
     
  11. usrjd

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    #11 usrjd, Jul 26, 2025 at 3:49 AM
    Might be getting somewhere - thanks to your circuit diagrams.
    Pulled the ECU plug to check continuity and restance between the water temp sensor (pins 71 & 74). Pin 71 is there in the connector - but not pin 74...
    It could have been pushed back into the connector, so either will peel back some of the loom covering to find the relevant wires and stick a pin through the outer insulation to check, or will dis-assemble the connector block from the plug housing and look inside (if I can get it apart after nearly 30 years!).
    More to follow!
     
  12. Qavion

    Qavion F1 World Champ
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    #12 Qavion, Jul 26, 2025 at 5:12 PM
    I rechecked my diagrams and they are the same as OEM.

    Would you be able to take a photo of the connector to see if there are any other variations? i.e. with the wiring loom on the RHS if that is possible.

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    Ferrari almost always show the rear of the connector, which is useless for sealed plugs, so I usually draw a reversed image to show the face of the plug.
     
  13. usrjd

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    #13 usrjd, Jul 27, 2025 at 4:20 AM
    Thanks for getting back to me - and I'll be happy to send photos of both of the ecu plugs (pin side) in the car. On my car (RHD UK Modificata) the ecu with pin 71 in place is on the passenger side along with the fuse/relay board.
    It'll take me a day or two to take the photos as the car is now up on the hoist with anouther underneath - I've finally run out of space...
    I'll send them across asap - and thanks again for the wiring diagrams, I don't know how you drew them!
    Cheers from Cairns,
    Richard
     
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  14. Qavion

    Qavion F1 World Champ
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    #14 Qavion, Jul 27, 2025 at 4:37 PM
    Last edited: Jul 27, 2025 at 4:52 PM
    Interesting. Doesn't make a whole lot of sense though. I assume the sensor and grounds are in the same position on the engine, so you'd want to keep the wiring for them going to the same ECUs.

    Normally there is a grounded pin telling the ECU if it is a Left (slave) ECU, so we may or may not see some differences there. However, I'm not 100% sure there is a master/slave setup on the 456M. Normally on Ferraris, the Immobiliser ECU only talks to the Right (Master) ECU and the R ECU sends an unlock signal to the L ECU. I just realised, however, that in the case of the 456M, the Immobiliser ECU talks to each ECU individually. Pin 88 is the unlock signal from the Immobiliser ECU on both ECUs.
     
  15. Qavion

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    #15 Qavion, Jul 27, 2025 at 5:05 PM
    Sorry, early morning here... I think I misunderstood what you said. Pin 71 is the ground for the coolant temp sensor (and other sensors) on both ECUs. Pin 74 should be the coolant temp sensor input into the ECU.
     

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