Hi,

My 2007 mk2 1.8 Duratec has a cooling fan problem.

 When the car reaches temperature, the cooling fan works as expected.  However, the fan does not stop running on slow speed until the ignition is turned off ( the temp gauge is working and the temperature is reducing) . A new ECT sensor has been fitted, but the problem persists.

If the car is left to cool for a while, the car will start without the fan, but it will come on again at the correct time and work as described above. 

If the car is cool, the air con will operate the fans as expected.

There is no designated relay in the fuse box, so i am guessing the relay control is at fault.

Any input?

if the AC switch is on at any temp above 3C ambient (and its all working),  the engine cooling fan will operate

on some Focus' this age they invented an electrically HEATED engine cooling system thermostat.... its designed to fail and make the engine die, the engine overheats because the stat never opens (once the heater element breaks), this causes the engine to run hot (but you should see the cooling fan cut in at high speed very frequently) as your is slow if its NOT the AC something else is going on

the rad and the ac condenser fills with crud at the bottom over the years and with other corrosion (salt and never being flush away) the upper parts of the rad will restrict air flow as well.  Both together will give impaired cooling capacity.  If you look outside its also rather hot, so its quite likely the cooling fan is running often.  If you turn off the AC (and or the gas has cause it to stop), the cooling fan with cut in and out noticeably at this time of year

You misunderstand. The car is not overheating,  it is over cooling. When the car reaches normal temperature, the cooling fan comes and the temperature will drop to 1/4 and the fan keeps running until the engine is turned off.  If the car is left to cool for a while, the fan will not turn on until the engine reaches normal temperature but then it will continue until the car is switched off.

I will back probe the fan signal wire later to see if there is power being sent from the PCM, but i suspect a faulty fan module relay.

over cooling is extremely unlikely in this weather

its possible you have the wrong temp reading in the car, and a fan running quite a bit in this temp sounds normal in this heat

if the AC causing the fan to run all the time is not happening (which augments the cooling of the engine) as not in use or broken, would mean the cooling fan comes in frequently (but I agree I don't think it will be slow speed) when my car had the thermostat heater fail issue, the temp gauge at all times displayed stable and normal temps.... but the engine was running hot !  the cooling fan was on high speed virtually all the time (even after 200m from cold start) a new stat (£110 quid and a total ***** to fit !!!) and has all been normal for 18 months