Radiator fan mystery

[alzmoore]

hello,

 

Just failed MoT because the car boiled up on the lift and so could not be emission tested.......the tester thinks that the fans didn't come on. (Strange that I could idle it forever and it never overheated but hey.....)

The first fault I found was that a voltage from the rear relay wasn't arriving at the front relay which was due to the little spade terminal in the front relay holder being pushed back so not making contact.  That got me to the point that if i send 12v from the back of the car to the front relay via the connecting wire the fans came on........however, I now find that I don't appear to be getting any input to the rear relay from the ecu so the fans aren't triggered.  This is the case even when the indicated temp on the dashboard is about 100C.  The sensor in the inlet manifold must be working, firstly because it's new and secondly because I have no fault codes and if it wasn't working it would affect other system and trigger fault codes.

So I'm baffled again.  Does anyone know at what temp the fans should cut in at? I understand that the thermostat opens at something like 82C but surely the fans should trip in by 100C???

[Sparky]

Fans should come in around 92.  You can't rely on the gauge; better to read the ECU for reported temp and go from there.

Unlucky, BTW!

[sailorbob]

The Delco ECU fan on temperature is 92 deg C.

Check the temperature the ECU is showing, the new sensor may not be working properly.

[CarBuff]

If the car was just serviced, verify that coolant is fully topped-off and bled. The cold level needs to be monitored for 5 - 10 drive cycles afterwards.

[alzmoore]

Thanks all.  Checked with freescan and ecu is seeing the temperature and it matches the gauge closely.  If I've got it right the ecu outputs 12v to the relay until the temp reaches 92C and then it earths which energies the coil relay???  Does that sound right?

It appears that there is no voltage arriving at the rear relay from fuse 13 at the front of the car so it looks like another broken connection from front to back....

[sailorbob]

The ECU only gnds the coil of the radiator fan control relay, the coil receives +12 V from fuse 21 on the SE.

[alzmoore]

Thanks..That make sense.  Jump wire from front to back seems to have solved it now....