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Cooling fan not working

Tiny
RAZVAN.JITARU
  • MEMBER
  • 2012 FORD FIESTA
  • 1.4L
  • 4 CYL
  • TURBO
  • 2WD
  • MANUAL
  • 70,000 MILES
I've changed the thermostat and the temperature sensor. I have changed the relays and fuses related with the cooling system. I have checked the fan itself and that resistor attached to the fan direct at the battery and they both work. The fan does not start when the engine overheats or when I turn on the A/C but if I disconnect the temperature sensor from the thermostat the fan starts right away. If is the PCM module do I get away with an update or do I have to replace it? Everything else works fine, no engine management displayed, no increased fuel consumption. Or can be any wiring from the PCM to the fuse box?
Thank you
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Saturday, July 25th, 2020 AT 2:56 PM

9 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay, this is a little misleading. When you are unhooking the ECT sensor the PCM is going into default mode and it turns the fans on. Basically it is programmed to just turn them on if it looses the ECT because it doesn't want to risk the engine overheating. So unplugging the ECT and the fans turn on does not condemn the PCM.

However, it very well could be a PCM for other reasons. Let's circle back to the relay. When you jump 12 volts to PIN 5 of the relay, does the cooling fan come on? Take a look at the wiring diagram and let me know this and we can go from there.
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Saturday, July 25th, 2020 AT 3:25 PM
Tiny
RAZVAN.JITARU
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  • 5 POSTS
Yes, it does start. I have checked both relays and the fan comes on.
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Sunday, July 26th, 2020 AT 7:52 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. So now we need to see if the relay is getting signal from the PCM to turn the fan on. So on pin 2 check to see if you have ground when the engine should be turning the fan on. So in other words, let the engine get hot and check to see if the PCM is grounding the relay. You do that but putting your red lead on battery positive and then the black lead on the relay terminal. Then when the PCM commands the fan on you should get 12 volts on the meter. This means the PCM is grounding the relay which closes it and it sends voltage to the fan to turn it on.

Let me know if you have questions on this. Thanks
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Monday, July 27th, 2020 AT 3:52 PM
Tiny
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Okay, so I have checked pin 2 with the black lead and the red on the battery's positive and the meter was reading 0. I have check the other ones the same and the only one who had 13 volts was pin 5. The temperature was 83 C I couldn't get it higher today. I will try tomorrow again to see if I can get the temperature higher than that. Thank you
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Tuesday, July 28th, 2020 AT 1:41 PM
Tiny
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  • MECHANIC
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Okay. If you have 0 volts on pin 2 then the PCM Is not grounding the relay to turn the fan on. Due to you already replacing the ECT sensor I would go ahead and replace the PCM because either something is telling the PCM to not turn the fan on or the PCM is just not able to turn the fan on. I would go with the PCM.
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Tuesday, July 28th, 2020 AT 6:36 PM
Tiny
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  • 5 POSTS
I checked again today and there was 9.73 volts in pin 2 with the A/C on.
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Wednesday, July 29th, 2020 AT 11:58 AM
Tiny
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I assume the A/C was still not coming on? If not then you either have a wiring issue causing high resistance of the an issue on the PCM circuit board. You need 12 volts to close that relay so my guess is even with 9 volts the relay was not closing which would point to one of these two issues.
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Wednesday, July 29th, 2020 AT 8:25 PM
Tiny
RAZVAN.JITARU
  • MEMBER
  • 5 POSTS
No, the A/C is not coming on. If I swap the PCM with a used one with the same number without doing any coding it will be alright? Just to see if the fan is working and I am sure the problem is the PCM and not some wiring. If is the wiring I will probably end up at the dealer and if is the PCM again I have to take to them to reset it so I will take it to them and see how it goes.I will post the result.
Thank you
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Wednesday, July 29th, 2020 AT 10:17 PM
Tiny
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Unfortunately you cannot swap this PCM. Once you do you will not be able to turn anything on as the security system will lock it out. When you put a PCM in newer vehicles like this you need to program it to this vehicle and the security system. A used PCM is going to have a different vehicle already in it and you will not be able to turn the ignition on and get the system to come on.

I attached the process for replacing it and you will see this info on step 5 of the installation.
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Thursday, July 30th, 2020 AT 6:06 PM

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