The car overheated when stationary or in slow traffic.  It was fine on high speed motorway and country roads.  The cause was quite simply a faulty radiator fan.  I replaced the fan which now works but only when the aircon is on.  For some reason,  I am not getting a current supply to the fan when the engine gets very hot.  When I turn the aircon on, the fan starts and the temperature drops very quickly.  So everything is ok except the trigger for the fan when the aircon is off.  The coolant temp sensor reads ok as I have checked this via the digital readout but will replace it tomorrow just to eliminate it.

Has anyone had this problem before or has a wiring diagram for the cooling system..  I am completely lost for ideas.

Thank you.

check the fan relay from the coolant sensor trigger, and check voltage going to the relay from the sensor when the engine is hot (at the relay) this will tell you if there is an issue with the sensor trigger wire

Thanks Neb for the inspiration.   Not sure if I have checked this correctly.  The relay is a simple 4 pin which I checked earlier to be working. There is battery voltage to the main supply terminal of the relay socket and when this is bridged to its opposite socket, the fan runs, so ok on those 2 sockets.  Of the other 2 sockets, one has battery voltage at all times, (cold or hot engine). The other socket, lets call it socket D, has about 4.8v when the aircon is off then 0v when the air con is on.  Hence enough potential difference to switch the relay and start the fan.

If I were to keep the aircon off, I get no difference in the voltage reading of socket D when the engine goes from cold to very hot.  But I think I should.

I am not sure what the above means or whether I should be checking something else.  Would socket D be connected to the coolant temp sensor or to the ECU. And if so is there another measurement to do.

also check the fan resistor, and check to see if there isn't a second fan relay

Thanks again.  I already checked for a second relay but there isn't one. I will do a resistance check on the fan tomorrow, but the fan works ok when 12v are applied to its terminals.

also check the two fuses are both not blown, also there is a resistor at the bottom of the fan case, that triggers the fan at the correct temp, check to see that it has not either broken or melted

Last time I had this problem it was the coolant temperature switch (the one for the radiator fan and not the one for the temperature gauge). It was just a two terminal sensor that was easy to change. It was an older Ford than yours so I can't tell you where it would be on your engine.

14 hours ago, Neb_engineer said:

also check the two fuses are both not blown, also there is a resistor at the bottom of the fan case, that triggers the fan at the correct temp, check to see that it has not either broken or melted

I had already checked the continuity of both fuses and they were good.  The fan doesn't have a resistor. It is a straight 12v to the motor.  Both old and new fans are the same in terms of design.  I believe that the trigger for the fan is the coolant temperature sensor which is fed to the ECU buy without a wiring diagram, I cant be sure.

14 hours ago, Matt Alsop said:

Last time I had this problem it was the coolant temperature switch (the one for the radiator fan and not the one for the temperature gauge). It was just a two terminal sensor that was easy to change. It was an older Ford than yours so I can't tell you where it would be on your engine.

Thanks Matt, I will be changing the coolant temperature sensor today, but don't think this is the problem.  I am getting good readings from the sensor.  Again without the wiring diagram, I cant be sure that another sensor does not exist.

Well the new coolant temperature sensor made no difference.  I found some wiring diagrams which shows that the CTS is wired directly to the ECU which then activates the relay which energises the fan.  Also my 2009 model does not have a resistor to control the fan, nor does it have two relays.  

I think the next stage is to look closer at the ECU terminals.

Did you get to the bottom of this problem? As I’m having the same problem with my 09 Zetec s

Hello Lee, welcome to the Ford Owners Club.

First question: Does your car engine overheat ?

My problem was a red herring.  It turned out that the fan did not come on even when the temperature reached 105C which is why I thought I had a problem.  The reason being is that the fan runs when the temperature reaches 106C.  I took the car to my local garage and ford specialist who ran the engine with revs high and the fan came on. Embarrassing for me.  When I got home I checked the temperature and sure enough it came on every time at 106C.  Or was it 105C?.

So as Unofix says, does your engine overheat.  I thought mine was but should have waited a minute longer or ran the engine at high revs and I would have solved the problem myself.

On 7/4/2022 at 5:01 PM, unofix said:

Hello Lee, welcome to the Ford Owners Club.

First question: Does your car engine overheat ?

Yes it does, but only while stationary or slow moving, I have to keep turning on the a/c to activate the fan

1 minute ago, Lee1583 said:

Yes it does, but only while stationary or slow moving, I have to keep turning on the a/c to activate the fan

If I don’t activate the a/c for the fan it just overheats and the coolant boils out

Hello Lee, thanks for answering the question.

This sounds like a simple case of a temperature sensor failure. The fact that the fan runs when the AC is on rules out a lot of other possibilities.

What engine do you have ?

If you know the location of the temperature sensor on your engine, then simply unplug it. That should cause the fan to start running (provided the engine is on).

41 minutes ago, unofix said:

Hello Lee, thanks for answering the question.

This sounds like a simple case of a temperature sensor failure. The fact that the fan runs when the AC is on rules out a lot of other possibilities.

What engine do you have ?

If you know the location of the temperature sensor on your engine, then simply unplug it. That should cause the fan to start running (provided the engine is on).

It’s a 2009 1.6 petrol. I’ve replaced the coolant temperature sensor and thermostat  (forgot to mention that) surely it can’t be a faulty new one? 

 

2 hours ago, unofix said:

Hello Lee, thanks for answering the question.

This sounds like a simple case of a temperature sensor failure. The fact that the fan runs when the AC is on rules out a lot of other possibilities.

What engine do you have ?

If you know the location of the temperature sensor on your engine, then simply unplug it. That should cause the fan to start running (provided the engine is on).

Hi fella, so I’ve just disconnected the temp sensor, fan came on straight away, plugged it back in and the fan didn’t shut off and the overheating light on the dash didn’t go off. 

47 minutes ago, Lee1583 said:

so I’ve just disconnected the temp sensor, fan came on straight away, plugged it back in and the fan didn’t shut off and the overheating light on the dash didn’t go off. 

So possibly you do have a faulty temp sensor, as when you disconnected it the fan was commanded on which is the fail safe operation.

PM me you registration number and I will see if there are any TSBs on the fan

12 hours ago, shabazmo said:

PM me you registration number and I will see if there are any TSBs on the fan

Oy09 zwj

what are tsbs?

TSB stands for Technical Service Bulletin. If there is an unexpected common fault on a vehicle, the manufacture issues a TSB explaining the symptoms and what checks to carry out and subsequent fixing procedure.  

I have checked and there are no TSBs for the fan not running.

Having a look at the wiring diagrams, there are 2 relays to operate the fan on some cars.  Probably one for when the aircon is on and the other for when the coolant temperature reaches 106C.  Early models had only one relay.  I would have said  check that you have both relays and check them both as one might be faulty.  But given that the fan turns on when the temp sensor is unplugged, the coolant temperature sensor must be at fault as mentioned above. Or there is gunge on the sensor which is not allowing it to detect the heat but highly unlikely.  change the coolant temp sensor again im afraid.

 

 

2 hours ago, shabazmo said:

But given that the fan turns on when the temp sensor is unplugged, the coolant temperature sensor must be at fault as mentioned above. Or there is gunge on the sensor which is not allowing it to detect the heat but highly unlikely.  change the coolant temp sensor again im afraid.

Agree 👍

Hello everyone,

I am experiencing the same problem with my 2009 Ford Fiesta. Despite replacing the coolant temperature sensor, the fan still fails to activate when the temperature rises. However, it does function properly when the AC is turned on or when I disconnect the temperature sensor. 
I would greatly appreciate if you could share your solution or let me know what component you ended up replacing in a similar situation.