🚗 Ford Fiesta 1.25 82 hp 2016 – Radiator Fan Not Triggering at Low Speed

Hello everyone,

I’m experiencing an issue with my 2016 Fiesta 1.25 82 hp petrol (Duratec 1.25 engine).

🔧 Issue Observed

• The radiator fan does not switch on at around 95°C, even though the engine temperature rises normally.
• It only activates directly at high speed around 105°C.
• Just before reaching that temperature, coolant starts overflowing from the expansion tank.

👉 It seems that the low-speed fan is not working, and only the high-speed mode activates as a safety measure when the temperature gets too high.

🛠️ Work Already Done

I have already replaced / checked:

• Thermostat
• Coolant temperature sensor
• Expansion tank
• Mechanical cooling system components (everything OK on the mechanical side)

The cooling system appears to function properly overall, with no visible leaks and no constant overheating.

🧪 Additional Tests Performed

• I can activate the radiator fan by turning on the air conditioning.
• I can also activate the fan using a diagnostic scan tool (OBD scanner).
• If I disconnect the coolant temperature sensor, the fan runs continuously.

This suggests that the fan motor itself is working.

⚡ Current Suspicions

The issue seems more likely to be electrical or control-related, possibly:

• Bad relay?
• Wiring/fuse issue?
• ECU not commanding low speed properly?

📄 Request

Could anyone provide the electrical wiring diagrams for the cooling fan system for this 2016 1.25 82 hp Duratec version?

Or advise on the priority checks for the low-speed circuit?

Thanks in advance for your help 🙏

There are several threads about a condition that SEEMS to exist when different trim lines of the same Model - in previous years, used a method of cooling the engine using a LOW-SPEED fan speed. Being; it's - using the same fan but thru a dropping resistor - which pulled air thru to cool the radiator at a lower volume to keep fluid cool but don't overburden the electrical side having to force air past the radiator at high-speed and raise noise levels to cause a form of concern (as in a panic). Only as - just a form of convenience not necessarily a required factor of quiet operation - but preparedness for dissipation of heat as a normal form of operation.

This Thread might help with this...
https://www.fordfiesta.org/threads/temp-sensor.8983/post-24610

For it helps reveal other threads that you can locate and even search for in using keywords like; Radiator and Low-Speed Fan to help find these nuggets in your searching.

Also the Resistor itself being composite and using a Thermostat Semiconductor - can also force the Solid State device - the Semiconductor - to fail shorted. Which would require the replacement of the whole radiator shroud housing or try and locate one in a junkyard as a working used replacement. You can remove the resistor/diode (semiconductor) and with some elbow-grease - clean the contacts and continue using it's remaining service life in your car's shroud.


The above is a "Catch-all" that can help explain the Hi- and Lo- speed operations and wiring to aid you in your diagnosis. It encompasses many other types of cooling and efficiency operation to help provide vehicles with more idealized temperature controls for the engine in both cooling in Hot weather as well as in Ice and Snowy colder weather to help keep heat in.

• When you are diagnosing this problem. Have you even verified the High-speed condition needed to make the FAN go high-speed even exists?
• - or does it come on all the time when you used to hear or experience the slower fan speed then it would go (sound noisy like it's on) high when it was necessary?
  • If you no longer have any low-speed operation - it just may mean the Diode in the Resistor assembly in the shroud has failed shorted - so it acts as a dead short ACROSS (In parallel with) the resistor - so the Low-Speed relay when it clicks on - does not see a load resistor to slow down the fan - instead the diode being shorted now makes the circuit see ground like a high-speed circuit and makes the fan work at High - speed - even when the condition requiring hi-speed - doesn't exist - the noise tells you otherwise

The Resistor/Diode Thermistor combo is only used when the Low-Speed Circuit Relay is engaged - it is bypassed using the Hi-Speed Relay when the PCM thinks things are getting too hot and catastrophic - it bypasses the Low-Speed and only runs High Speed.

How to check? Remove The Low Speed Relay - if the Hi-speed fan stops - there's your condition - the Module has failed.

Thank you for your response, Handy Andy.
The radiator fan assembly has already been replaced, so I do not believe the issue originates from the fan motor itself.
To address your questions:

• The cooling fan engages directly at high speed (loud operation) when the coolant temperature reaches 105°C.
• When the coolant temperature sensor is disconnected, the fan immediately defaults to high-speed operation.
• The low-speed stage of the cooling fan no longer activates under any operating conditions.

Based on these observations, it appears that only the high-speed circuit is functioning, while the low-speed control stage is inactive.

As you suggested, I will proceed with checking the low-speed relay circuit as the next step in the diagnostic process.