Radiator fan

Hi all.

I've had this issue for a while, typically as the warmer weather has put in an appearance, it's now getting a bit unbearable.

My radiator fan does not come on when the engine gets hot.
It works with the air-con and will come on if I pull the plug off the coolant temp sensor (under coil pack).

I'm sure the fan should have been on at this point...:



Is the rad fan is controlled by a relay... but if this is faulty, wouldn't the fan stop working completely?

Just a guess but wouldn't it have to be a faulty sensor if the fan is capable of working in other circumstances including when its disconnected from the sensor?

quest63 said:

Just a guess but wouldn't it have to be a faulty sensor if the fan is capable of working in other circumstances including when its disconnected from the sensor?

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Typical that would be, the sensor is new as I changed it trying to solve this issue before.

Is the fan not ecu controlled, have you check for voltage down the wires and resistance?

Yes, I think the fan is ECU controlled.

I can't find an electrical diagram on my TIS for the engine cooling system. That's not very helpful.
Think I'll start by looking to see if the relays are seated properly.

Thats a nuisance when that happens, it takes a leap to presume a new bit is faulty,but if the ecu is recognising when the plug is disconnected then it would seem that the wiring that passes the temperature signal to the ecu must be intact and therefore it must be the sensor at fault. Was it a Ford part?

Is it just two wires to the sensor I suppose you could have two wires sending the temperature signal and another two wires monitoring continuity of signal so that the fan defaults to on if a sensor connector comes off or breaks, in which case the above wouldnt apply.

Can you measure it electrically when its cold and then at stages as it warms up I would guess if the sensors faulty its output or resistance or its warp factor or whatever lol wont change

Found a wiring diagram :thumbs: Wasn't where I thought it would be!

The sensor was bought from EuroCarParts. It's a 'two wire' job so I can only assume it works on a resistance basis. I could check it's resistance as the engine heats up, but I don't fancy my chances of accurately measuring that right underneath the coil pack, while it's still connected to a vibrating engine and more so without burning myself.

So, as for how the ECU could read the resistance from the temp sensor:
There would be no point in the ECU not sending a voltage to the sensor otherwise it would not do anything, so I can assume the ECU sends a constant voltage to the sensor.
Now, bearing this in mind, the sensor would be resistance based and could be explained like this:
Cold coolant, low/no resistance: ECU gets a return voltage.
Hot coolant, high resistance: ECU gets no return voltage.
So we could deduct after that, that unplugging the coolant sensor and creating an open circuit, would force the ECU into thinking the coolant is hot (no resistance on sensor) therefore knocking the fan on.....

Phew! Does that make sense..!?

Hmm good point, maybe pull it out and test it in the house while slowly heating up a pan of water :thumbs:

quest63 said:

Hmm good point, maybe pull it out and test it in the house while slowly heating up a pan of water :thumbs:

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I hate it when people come up with a smart answer!! lol

So, out comes the sensor, so coolant loss again... Wouldn't mind so much if the damn cars didn't like to air-lock!

So, as for how the ECU could read the resistance from the temp sensor:
There would be no point in the ECU not sending a voltage to the sensor otherwise it would not do anything, so I can assume the ECU sends a constant voltage to the sensor.
Now, bearing this in mind, the sensor would be resistance based and could be explained like this:
Cold coolant, low/no resistance: ECU gets a return voltage.
Hot coolant, high resistance: ECU gets no return voltage.
So we could deduct after that, that unplugging the coolant sensor and creating an open circuit, would force the ECU into thinking the coolant is hot (no resistance on sensor) therefore knocking the fan on.....

Phew! Does that make sense..!?

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I'm having to assume the above is written in some kind of ancient hyroglyphics or swaheli,but whatever it means I'm sure your right :thumbs:

quest63 said:

I'm having to assume the above is written in some kind of ancient hyroglyphics or swaheli,but whatever it means I'm sure your right :thumbs:

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Erm, not really. Just my usual dribble!! :zzz:

Its damm good dribble I'm buying it lock stock and barrel with a side order of fries Oh hell can you supersize it :grin:

quest63 said:

Its damm good dribble I'm buying it lock stock and barrel with a side order of fries Oh hell can you supersize it :grin:

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I could, but I don't think I'd have the patience to sit here that long!!

Anyway, back to the subject in hand... I've just been out and had a look at the relays. I've taken them out and cleaned the contacts, but don't know what else to look for regarding them.

Check the earth connection on the bottom of the frame. Just follow the wires from the fan motor. If it looks a little mucky/rusty then give it a clean.

scbond said:

Check the earth connection on the bottom of the frame. Just follow the wires from the fan motor. If it looks a little mucky/rusty then give it a clean.

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Good suggestion... nice one. Thanks!

Just speculation but seeing as the fan works when the sensor is disconnected if you assume its a relay problem then either it would have to have a second relay to make it work based on temperature (thats not working) or it would have to have a relay with two circuits through it, one for the ecu to switch it on when the sensor is disconnected,and another circuit to switch it on based on temperature (thats not working). I dont know how likely that is

topmansparkie said:

scbond said:

Check the earth connection on the bottom of the frame. Just follow the wires from the fan motor. If it looks a little mucky/rusty then give it a clean.

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Good suggestion... nice one. Thanks!

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Thinking back, I don't think that would help as the fan does work, but only on slow speed with the air-con and if I unplug the temp sensor.

quest63 said:

Just speculation but seeing as the fan works when the sensor is disconnected if you assume its a relay problem then either it would have to have a second relay to make it work based on temperature (thats not working) or it would have to have a relay with two circuits through it, one for the ecu to switch it on when the sensor is disconnected,and another circuit to switch it on based on temperature (thats not working). I dont know how likely that is

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As stated, the fan works on slow speed with air-con and unplugging the temp sensor.
There are two relays. One for slow speed and one for fast speed. As it works on slow, I'm assuming the relay works.
At what point it comes on high speed, I have no idea, but either way the ECU controls it.

The ecu will send the signal to the relay, which in turn fires the voltage to the fan if that relay is stuck open the fan won't work likewise if there is a break in the signal wire it won't work

Ginger Tom said:

The ecu will send the signal to the relay, which in turn fires the voltage to the fan if that relay is stuck open the fan won't work likewise if there is a break in the signal wire it won't work

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Is the relay stuck if it works on AC?