Hi All,

I have just bought a 2008 1,4  MK6 Ford Fiesta, The issue that I have is that, the radiator fan is on as soon as I start it from cold and stays on at high speed. this will turn off as soon as the engine is off.

I have swapped the cooling fan relay, but would like confirmation as to which one this is,so I am changing the right one ! as mine is not by the battery and I have changed the cooling temperature sensor.

Anyone any ideas of what this could be, also this model has air con, which currently is damaged and not operating properly.

Thanks

John

How many relays do you have in the relay box by the battery?

One the one, its black

Sorry that was one😀

If you take the connector off the temprature sensor does the fan stop ?

Since I Installed I have not checked, but I will check this and let you know.

👍

Alright Mate,

I have removed the plug connector off the temperature sensor and the fan keeps running.

If you take the connector off the temprature sensor and the fan Stops then you have a faulty sensor (or the wrong one). If with the sensor disconnected the fan is still running then the cause is probably a stuck relay which I think is R8 in the inside fuse/relay panel.

See YouTube video

 

Thanks for that I will replace it and let you know what happens

First remove relay 8, do not replace it. Does the fan stop with relay 8 removed ? if yes then you have found the correct relay for the fan. Fit a new relay.

If you remove relay 8 and the fan still runs it probably means it is not the relay for the cooling fan.

33 minutes ago, unofix said:

If you take the connector off the temprature sensor and the fan Stops then you have a faulty sensor (or the wrong one). If with the sensor disconnected the fan is still running then the cause is probably a stuck relay which I think is R8 in the inside fuse/relay panel.

See YouTube video

 

Above description is incorrect.

If the temperature sensor is disconnected the fan will run continuously. It is a fail safe feature.

Seeing that you have just obtained the vehicle, I would check that the engine management light works. It should come on when you turn the key to position II and go off when the engine is started.. 
 

Edited April 12, 20215 yr by Dan62
Modified

Hi Dan62, well assuming I'm wrong and your right then the simple way to test the sensor would be remove the connector and using something like a paperclip short the two wires on the connector together and the fan will stop if the sensor is at fault, otherwise we are back to the problem most likely being the relay 😀

 

6 minutes ago, unofix said:

Hi Dan62, well assuming I'm wrong and your right then the simple way to test the sensor would be remove the connector and using something like a paperclip short the two wires on the connector together and the fan will stop if the sensor is at fault, otherwise we are back to the problem most likely being the relay 😀

 

Its a sensor, not a switch.
The sensor is a resistor (NTC) which connects to the PCM. The PCM uses the sensor for the temperature gauge and for switching on the cooling fan.
If the sensor is either disconnected or shorted out, the PCM will start the fan, it will also bring on the engine management light and log a DTC.
If it was a thermal switch I would agree with you, but its not.
And I don't think it will be a stuck relay either as turning the ignition off stops the fan.

Thanks for the update Dan62, I thoght the 2003 Fiestas still used a thermal switch, I hadn't realized they had become Hi-Tec. This new information kind of puts the whole thing in a different light. Pulling the relay (possibly R8) should kill the fan dead. If it does then at least we know that is the correct relay for the cooling fan. The relay must be getting turned on by the PCM either because the PCM is at fault or that the information it is receiving from the sensor is wrong.

Do you know the normal cold resistance of the temprature sensor ?

Sorry to butt in, but is there not two relays for the fan ?

One initiated from the CTS through ECU to one relay, R8 internal fuse box, and another, R2 by battery, that is controlled by the air con ?

Hi Paul, thats a good point you make. Is it a case of either relay can turn the fan on, or does it need both relays to be energised in order to turn the fan on?

Given that its a Fiesta Climate you might be right about R2 by the battery box.

I have read before where fiesta's of this age don't have the high speed relay in the battery relay box and don't have the cooling fan resistor, but do have A/C.
Seems only 1 relay in the box which must be the WOT A/C relay.

Hi,

Thanks for all the info on this I am still awaiting the arrival of the relay to try it, but just to clarify of what is mentioned above, am I looking at two relays ?

I know about the one on the fuseboard which is R8, but isn't the other by the battery an air-con relay, if this one had gone, would it affect the fan.

Also what Dan62 mentioned what is a WOT A/C Relay.

Thanks need all the help I can get.😀

What is a WOT relay?

Description. The logic module uses this relay to disengage the air conditioning compressor clutch when the throttle position is at wide-open (WOT). ... Lastly, it is used to disengage the clutch if the engine speed drops below 500 rpm, to try and keep the engine from stalling.

 

I think you can probably discount a problem with this. 🙂

I have just changed R8 Relay and the fan is still on high speed only when the car is running again.

So I think this can be discounted, my fan does appear to have damage to it, due to it being a cat c car, so I think I may change the fan out, see if this alters things, as the resistor may be playing up, just a thought.

John

NO !!

The fan is fine, do not your waste time and money replacing the fan.

With Relay 8 removed did the fan stop ? I'm going to assume yes. So the problem is that R8 is being energised. Have you any means to check the fault codes "DTC" ?

 

 I am going to change the fan anyway as its damaged, which is common sense as you can rule this out, and I already have one.

Also I can see if any fault codes come up when I check it later.

Thanks for the Info on but am still going to change the fan unit.

John

Again thanks for your help, but I will keep on looking. 

let us know if there are any fault codes when you check. If the car has been in an accident at some time I wonder if the wires to the temprature sensor may be damaged?

"Anyone any ideas of what this could be, also this model has air con, which currently is damaged and not operating properly."

I'm under the impression that switching AC on, turns the fan on full, so is this where the problem may lie ?

Digressing back to the CTS, Haynes states 20deg =6100 ohm, 80 deg=620 ohm.

I understand that either relay will start the fan.