Ford Focus Radiator fan not working in response to high temperature

2001 Ford Focus Problem

Ref#19856
CarFord Focus 1.6L petrol with a/c
Year2001
OwnerFrancisB
Posted09/08/2016
Ads by Google
The engine overheated recently. The safety facility worked well and the engine started firing on two cylinders. That warned me that something was wrong and I noticed the temperature gauge was in the red region. I pulled over and saw that the coolant was low, so I added water. I was able to get home without the gauge going high again, but to cut a long story short, I found several faults: a burst heater hose, a burnt contact on the fan resistor connector, the left hand fan motor defective and the thermostat not opening properly! (Is this a record?) There was an engine overheat fault displaying. It disappeared after disconnecting the battery.
I blocked off the heater since I couldn't find the proper hoses, I ordered a thermostat and ran the car without one (not a serious problem as it is hot here), I bridged the connector to eliminate the burnt contact, and replaced the left hand fan with a generic one. I replaced the thermostat finally and was surprised to find the car overheating again. Removing it and testing it alongside the old one revealed that the new one was only opening to about 5mm, just as the old one had done when I tested it previously. Now, however, the old one was opening to a good centimetre. It seems the new one is defective! I'm back to running without the thermostat - which seems to have affected the fuel consumption somewhat - it's down from about 40 mpg to about 37 mpg. I have also confirmed that the fans are not coming on as expected. I normally run with the air conditioner on, and that causes the fans to come on, which helps with radiator cooling, but on idling without the air conditioning on the engine overheats but the fans do not come on. Both relays seem to be operating normally: removing either one affects the fan speed when the air conditioning is on, and removing both cuts off the fans entirely. Shorting contacts 3 & 5 on the relays causes both fans to come on as expected. Testing outside the vehicles shows that the relays are working properly. All fuses are OK. The temperature sensor (situated in the cylinder head) does not seem to be the problem - connecting my tablet via a dongle shows the temperature behaving as one would expect and the engine slows down normally on warm up. Under normal running the temperature stabilises to about 80 to 90C. (The original and replacement thermostats open at 82C. I don't believe that they are two-stage types.)
So, I am stumped! Why aren't the fans coming on at high temperature? Could it be a problem with the computer (PCM)? It seems unlikely, since everything else seems to work normally. Perhaps a bad contact somewhere? That seems unlikely since the fans come on as expected when the a/c operates. Perhaps the sensor, but then the temperature gauge on the dash and the readout on the tablet seem fine. Any suggestions?
Problem Category
Electrics, ECU, Warnings & Lights


Solution 1
whittingehame | Legend | Since: Oct 2009 | Posts: 444 | Fixes: 11466 | View Garage
Suggested Solution

Coolant fan resistor on fan shroud o.k?


Posted on Wednesday 10th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

Yes, that was one of the first things I checked. I am beginning to think it must be the PCM, since I seem to have eliminated everything else, but is this possible when all other functions seem to be fine?


Posted on Wednesday 10th of August 2016
Don't understand this? Ask a question
Solution 2
whittingehame | Legend | Since: Oct 2009 | Posts: 444 | Fixes: 11466 | View Garage
Suggested Solution

I would change the easy / cheap sensor in the head , the temp gauge is a different sensor ( as far as I can remember ) , so may be reading o.k .The engine will not be reaching operating temp without thermostat , hence mpg drop .


Posted on Wednesday 10th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

There is only one sensor according to the manual. I suspected there might be more than one as you suggest, but have not been able to find another one. It is a two-wire sensor, so it is possible that one gives a temperature reading and the other a control signal for the fans, but the manual suggests otherwise.


Posted on Wednesday 10th of August 2016
Don't understand this? Ask a question
Solution 3
whittingehame | Legend | Since: Oct 2009 | Posts: 444 | Fixes: 11466 | View Garage
Suggested Solution

The wire to the cylinder head temperature sensor fitted on some Zetec 1.6 engines , between no 2 and 3 ht leads o.k ?


Posted on Thursday 11th of August 2016
Don't understand this? Ask a question
Solution 4
1/4drive | Auto Insider | Since: Jun 2011 | Posts: 25 | Fixes: 1539 | View Garage
Suggested Solution

Head temp sensor is two wire,
Brown/white is the 5V feed shared with other sensors which would give poor running and fault codes if faulty.
Other CTS wire is white/violet which is the temperature corrected signal back to the PCM.
Situations like this I unplug the CTS and plug a variable resistor,
Basically a volume control from Maplins.
in the harness.
Possible now to vary the signal manually and hopefully "drive" the CTS signal to the PCM and force the fans to work.
Or not is the PCM is faulty.


Posted on Thursday 11th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

Thanks. I disconnected the sensor today. I had tried before but the connector is inaccessible and I had had no luck with the camshaft cover in place. I bit the bullet today and removed the camshaft cover. A sod of a job! I see that I could have released the connector by slipping a skinny screwdriver under the little plastic bridge on the side of the connector before pulling. When I started the car, after a short delay the fans started, slow at first, then full speed after a second. That suggests the PCM is OK. I haven't yet tried connecting a variable resistor, partly because I am not sure how to connect it. Should I just connect it between the 5v rail and the wire to the PCM? Or should I connect the third terminal of the resistor to ground as well? A 50 kohm resistor should do?


Posted on Thursday 11th of August 2016
Don't understand this? Ask a question
Solution 5
1/4drive | Auto Insider | Since: Jun 2011 | Posts: 25 | Fixes: 1539 | View Garage
Suggested Solution

You don't need to do the variable "R" test now as you've proved the PCM is sending the fan Go signal.
CTS faulty.


Posted on Friday 12th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

I now see that i have the appropriate circuit diagram. (Boy! These Ford Manuals are opaque! I can't even do a word search on the one I have.) The temperature sensor is just shown as a variable resistor between the two wires you mentioned: white/violet and brown/white. I think I'll try your suggestion anyhow, to see what it does. Thanks very much for your help!


Posted on Friday 12th of August 2016
Don't understand this? Ask a question
Solution 6
1/4drive | Auto Insider | Since: Jun 2011 | Posts: 25 | Fixes: 1539 | View Garage
Suggested Solution

Actually I can't agree,
Ok Ford manuals are different but once you get used to them I really like them.
You should have seen what passed for wiring diagrams from Autodata back then!
If it's any help I got the wiring details from WOW,
That's Wurth's answer to autodata.


Posted on Friday 12th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

I take your point, but it's a steep learning curve. Maybe I have an old product - something that runs under VMware - but still, one should at least be able to search for a term like "radiator fan" or "temperature sensor". The diagrams are pretty useless too. I have a diagram for the position of the PCM, but I can't make out where it is. What is "WOW"? When I Google it I come up with things related to "World of Warcraft". LOL It took me an age to find the wiring diagram for the cooling system, and then there is no key to explain the symbols. For example, I'm still wondering what lines ending in solid triangles mean. They aren't grounding points. They don't seem to mean that triangles are connected to each other. If they were test points there would be voltages or similar. Any idea?


Posted on Friday 12th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

I connected the resistor between the two sensor wires as suggested above. I monitored the temperature that the computer reported with my tablet via a Bluetooth link to an OBD dongle. The fans came on at a temperature of nearly 240F! At this temperature the dash indicator is in the red! I think this temperature is way too high. Surely the PCM must be faulty. Can it be reprogrammed or must it be replaced?


Posted on Sunday 14th of August 2016
Don't understand this? Ask a question
From Original Poster
FrancisB | Driver | Since: Aug 2016 | Posts: 0 | Fixes: 3 | View Garage
Suggested Solution

I have solved the problem! Originally the fans wouldn't come one even under an overheat condition, but after checking the operation of the computer by replacing the temperature sensor with a resistor, the fans seemed to be working. They came on at a simulated temperature of about 240 F. The gauge read high at 255 F, and was in the red by 266 F - it was difficult to adjust the simulated temperature precisely. The problem that remained was that with the thermostat in place the engine quickly overheated. (In the meantime I had a leak from the thermostat housing, which was due to a damaged seal. I think I must have damaged it trying to withdraw the housing without disconnecting the hoses. I was able to replace it with two standard o-rings, one on top of the other, and a bit of silicone to hold the outer one in place. I also discovered that you don't have to remove the serpentine belt before removing the alternator, saving a lot of time - one has to remove the alternator to get at the thermostat housing.) I think I mentioned that I had disconnected the heater, since the hose had burst. (That probably precipitated the original overheat.)
Someone said that the heater provides quite a bit of cooling. I must admit I didn't really believe that, but since all else had failed, I decided to try reconnecting the heater. I had to use generic hoses, which was a slight problem because on one hose the two ends are different sizes. Anyhow, it cured the problem! Now the engine maintains a temperature close to 220 F (105 C), just as one post mentioned, but I can't see why. It is very surprising to me that the thermostat is adjacent to the inlet from the radiator, at the bottom of the engine. That had me thinking that the flow was out of the bottom of the engine to the top of the radiator, but the temperatures of the pipes show otherwise. It rather appeared that the thermostat was not opening with the heater disconnected for some reason. Perhaps someone can explain.
There seems still to be a slight leak of coolant. I am hoping that it is not the cylinder head gasket that has been damaged by the overheat!
One other lesson I learned was that the reservoir cap must be tightened down really well to maintain pressure. That might have been responsible for some of my problems, since a low pressure would allow water to boil and could produce vapour locks, and interfere with cooling.


Posted on Thursday 18th of August 2016
Don't understand this? Ask a question
Ask a Question Post a Solution


More Ford and Focus problems

Ford Problems Focus Problems

Social Media

Twitter Icon Facebook Icon Google G+ Icon

Car Problems - can you help?


Run an Auto Business?