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UltratechOne
UltratechOne, ASE Certified Technician
Category: Car
Satisfied Customers: 46
Experience:  General Automotive technician for 39 years. ASE certified. Shop Owner and MBA.
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Land Rover Freelander: Dear Expert: Freelander 2003 V6 petrol. The

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Dear Expert:
Freelander 2003 V6 petrol.
The Engine cooling fans are not starting and the car is getting overheat.
I understand they have to start because of high temp but "also"if we turn on the AC.

Happens that I turned on the AC but didnt start, only after 10 seconds it make some turns at low speed and after stop again.
Somebody told me if we disconnect the sensor located in the lowe hose of radiator, the fans should start because of safety reason and to avoid overheat when the wires of sensor are broken.
The fans are ok, because they run if we connect power directly.

do you think is hte ECU or control unit located in the midle of the fans? IS true that when we disconnect the sensor the fans should start?
rL.

UltratechOne :

hello,my name is XXXXX XXXXX i'll be helping you today.

UltratechOne :

the cooling fans on your vehicle have several ways to be activated. first is of course when the coolant temperature rises above a certain point. second is when the a/c is turned on they should come on immediately in order to cool down the condenser.

UltratechOne :

as i understand it the fans dont come on at either of these times which would indicate a break in the voltage or ground from the fans themselves to the activation point.

UltratechOne :

by disconnecting that sensor, the fans would not come on at all when the system is operating normally. so don't do that.

UltratechOne :

however, to diagnose you will need to remove the connector from one or both of the fans and test for voltage when you turn on the a/c. next, test for a good ground at the connector. my guess is you will find no voltage when the a/c is on and you will need to trace backwards to the computer (which turns on the fans) and find where you are losing the signal. you will also need to verify that the computer is outputting voltage to turn o the fans when the a/c is on. if it is you need to look for the break and repair it. if it isn't the most likely scenario is a sensor is not telling the computer to turn the fans on such as a temp sensor and/or a a/c clutch engaged sensor.

Customer:

Ok, the information you said about disconnecting the sensor not start the sensor is useful for me.

UltratechOne :

check your control unit between the fans by testing for inout and output voltage. the least likely problem is a bad ecu so save that for the very last.

UltratechOne :

yes, that won't help. it is just sending a signal to the computer and if there is no sgnal (by you disconnecting the connector) the computer will default a value and the fans won't come on.

Customer:

Any way to test the ECU control unit in midle of the fans? When we start the AC the ECU also act for start the fans?

UltratechOne :

you'll need to verify which terminal has battery voltage. the control unit works by getting a ground supplied by the computer so that it pulls in the relay which then sends voltage to the fans.

Customer:

Any way to troubleshoot the input of ECU? o;r input/output?

UltratechOne :

so check to see if you have battery voltage thee at the control unit when the key is on. you should. if you don't check for why there is no voltage there.

UltratechOne :

without a scan tool there really is no way of looking at the data stream the computer is seeing. do you have a scan tool?

UltratechOne :

i'm going toask something very obvious - you have checked all the fuses with a test light, right?

Customer:

Nop, I dont have Im at home at not mechanic. I understand is not only a relay but also control speed of the fans

Customer:

is that true?

Customer:

MEans that is not only a on/off switch but a speed control

UltratechOne :

yes, it is true. it is most likely the problem, but i don't want you to replace it unless you've exhausted the other possibilities. so here's the best way to approach it - make sure you've checked all your fuses - the voltage supply forthe control unit will go through at least one fuse. check for voltage at the control uunit when the key is on. if there is voltage there, then the most likely cause is the control unit itself.

UltratechOne :

since the fans don't work with the a/c or temperature rise that says it's unlikely it's a sensor problem or ecu. i'm really leaning toward the control unit itself or a bad connection or fuse.

UltratechOne :

basically if you've got voltage to the control unit, then it's almost for sure the control unit is bad. if you don't have voltage to the control unit you need to find that problem. you could even verify operation (if there is no voltage at the control unit) by supplying voltage temporarily and observe the operation of the fans. but i still think you have a control unit problem. are you clear on how to proceed?

UltratechOne :

i'm going to jump out to the q&a mode so i'm sure you're getting my answers. please let me know if you have any further questions and i'll be happy to help. and don't forget to rate my help today 5 stars so just answer will pay me for my time. thanks and best of luck with your fan problem! please let me know when you fix it. :)

Customer:

I think not fuse because its turning . (at low speed and few seconds but running)

almost for sure you have a controller problem then.
hello rafael. please don't forget to rate my answer 3 stars or higher and don't hesitate to ask anything further on this question. thanks! :)
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