4 wire harnass 3 pin cooling fan

[Brandy01]

Hi guys,I have a 1996 Golf Mk3 Gti 2.0L 8v AFW ,my cooling fan (I have the dual fans connected with belt) only comes on at high speed,no low or med.

My car has the additional blue coolant temp sensor inline with the "standard" yellow temp sensor,the blue temp sensor is apparently for the high speed of the cooling fan.My problem is that the wiring harnass to the fan has 4 wires but my fan connector only has 3 pins. Seems the car was in an accident previously and they replaced fans.
The four wires coming from the harnass are
red/white
red/black
red/green 4.5/5mm thickness
brown/green 4.5/5mm (this one is not connected)
Should the brown/green be connected? Or is my fan issue caused by something else?
Maybe the FCM causing it because it had gotten wet before,I unplugged it and cleaned plug connectors etc
Please if somebody can give me guidance

[panic-mechanic]

the temp senders don't directly control the fan. ie. it's not one temp sender for high and one for low. The fan is controlled by the fan control relay - that thing sitting under the water bottle and that is likely your issue.

[Brandy01]

Sorry for the delay in response but thanx,I actually opened the relay/Fan cntrl module on Sunday and very carefully cleaned the contact points inside with very fine sandpaper and alcohol because they were dirty,but nothing was fried or anything like that.
The extra wire not connected on the fan harnass,should it be connected,if possible on 3 pin?
Apparently the 4 pin has 2 ground and low an high spd,Haynes says 3 spd switch which I'm assuming is the 2nd coolant temp sensor. Im not saying you are wrong though,that it could be fcm! Below is what Haynes says.

Note: On some models equipped with air conditioning, there is also a second switch (fitted into one of the coolant outlet housings/hoses on the cylinder head). This switch controls the cooling fan stage 3 speed setting.

[Brandy01]

I think i may have found my issue for the fan as well as being part of my erratic idle problem. My manifold
Air temp sensor,the one screwed into a bracket which is attatched to the front underside of intake manifold (not the ambient air temp sensor in the rain tray), only has one wire,Brown/Black, attatched to the sensor. This morning i unplugged it and touched the manifold by mistake and my radiator fans gave a short turn. Can I just ground the sensor ? Surely it eill be ok?
Then i just need to sort out that extra wire in fan harnass

[Brandy01]

Anybody?? Looking at my posts now,1) I was wrong about the sensor attatched to the outside of the intake,2) The question I should have asked is
:Is it possible to get all 3 speeds working with a 3 pin plug on the fan (which is actually a 2 pin which was obviously replaced at some point)My high speed wire (6mm red/green) is not connected,suppose i will have to choose which speed to leave out.
3) Do I leave low or medium speed out? Obviously better to have high and...
I just need a definite answer although I think I know the answer.
Please guys

[panic-mechanic]

At best they had 2 speeds - you cannot make a 3rd one without designing something yourself if you are an electronic wizz.

[Brandy01]

Im not saying you are wrong,but why do I have 2 coolant temp sensors inline then? They are both
4 pin so the need to have a sensor for guage and another for ecu is not needed anymore because
these 2 are now incorporated into one 4 pin.Also,together with this I also have the 4th wire in fan harnass
which is for the fastest speed. I come from a carb background and only changed to fuel
Injection beginning this year,so Im still learning..

Here is a pic of the 2 sensors. The wiring&plug for the 2nd sensor was just hanging when i got the car..
http://s86.photobucket.com/user/brandy0 ... sort=1&o=0

[Brandy01]

This is from the Haynes manual
http://s86.photobucket.com/user/brandy0 ... sort=1&o=0

[MK2 G60]

The system works like this. One switch is for the temp sensor and the other the gauge.
The second sensor is usually for the air-con system so it knows what temp the water is at. It needs this input and the ambient temp as the system cannot function under a specific temperature eg -4 deg. If there is a error in this system air con will not work.
The switch you reff to on the manifold is for fan run on when the manifold it really hot this was put in place to prevent fuel peculation in the rail and damage to injectors in some cases. Don't grond the wire or fans will always run.

[MK2 G60]

As for the fan speeds there was diff types of diagrams and lay out.
The common one was the thermos switch on the radiator controls the first and second speed of the fan. Fan has three wires usually a common ground and the two power supply wires that run to the box under the chassis leg.
The first stage of the thermos switch is at about 96 deg and sends the signal to the box and that closes the relay for first speed [air con will also send signal for first speed to the box if it is turned on]
The second speed is activated via the thermos switch too and operates above 98 to 101 deg , this was mostly for when the air-con was on and the first stage could not cool the car due to added load.
I have only seen third stage on t3 bus and one or two select mk3 units. There was not really a need for three stages on the local vw units,
If yours only comes on on 2nd stage look at the thermos switch and also see if fist stage works with air-con on if it still works if not don't look at the circuit. If thermo switch fine look at the signal wire to the box. The box can also look fine but you don't know what the coil windings look like inside to close the relays.