Cooling fan fault?

sounds ok to me.

Ok this is the G62 sensor, which is the coolant temperature sensor. This is a fairly common failure, - or at least it has a reputation for failing, and the fact they brought out an updated replacement would suggest this is true.

The original sensor is black in appearance, the updated part has a green top. You will commonly read or hear of people refering to a green tops sensor.

These are an easy DIY replacement and not to expensive. However a dealer may charge you around £25, an indpendant parts place like GSF will likely charge around £10-£20 i think.
Im sure if you go in anad say i want a green top tenp sensor they will know what you mean, but otherwise they can look it up.
But part number is: 059 919501A

Where is it?
well if you pop the bonnet, then looking at the engine its to the right side of the engine, between the engine and battery. (may need to remove plastic cover on top of engine)
Its in a coolant pipe and from memory the sensor top faces upwards with an electrical connection.

Simply remove the electrical connection, then slide off the plastic retaining clip, pull out, (you may get a tiny spil of coolant but nothing to worry about) then pop in the replacement.
Make sure its got the rubber o ring on it.
part for rubber ring is: N 903 168 02

reconnect sensor, and jobs done. no resetting or anything needed.

pic shows two green sensors, the far sensor has the plastic clip on it. (U shaped part)
http://media.photobucket.com/image/green top sensor/Spikee4u/DSC00894.jpg

realman wrote


At present the small fan runs continuously when the air con is on. With the air con off my liquid display will go up to 105 0C before the small fan cuts in. The fan will only run for a minute untill the temp goes down to 100 0 C. The temp gauge in the dash never moves of 90 oC (when warmed up)

When should the larger fan cut in?

Should both fans come on together?

Yes

At what temp should is go to fast speed?

on: 99...105 °C
off: 91...98 °C

where is the sensor which controls the fans? is it the same one as the gauge in the dash?

Not at all. It is a thermoswitch in the radiator itself, the sensor unit contains two switch devices which exhibit hysterisis, i.e. they switch on at a certain temperature but then don't switch off until a lower temperature has been reached.

With the air con switched on the engine never over heats my liquid gauge shows between 75-90 oC.

It could well be a faulty thermoswitch, wiring, or a fan control unit gone wrong.



The radiator fans are controlled by a thermoswitch in the radiator itself. You can remove this and stick it in a saucepan on the stove, with a thermometer, and check that it performs as specified:

1st speed
on: 92...97 °C
off: 84...91°C
2nd speed
on: 99...105 °C
off: 91...98 °C

Remember, these are temperatures in the top of the radiator itself.


In cars with cabin air cooling ("aircon"), both fans should run at low speed when the air cooling compressor is engaged ("snowflake"). There is a separate fan control module under the battery tray which combines the thermoswitch output with a signal from the Climatronic to say that the compressor's on.

The Coolant Temperature Sensor that Andycupra's on about has nothing to do with controlling the radiator fans. The radiator fans are controlled completely separately from the ECU (unless you have aircon), by a system that could be fitted to a car with no electronic engine control at all.

The CTS has two sensors in one unit, one feeding the dash gauge (only) and the other feeding the ECU.

hmmh, when my aircon is on, just the small fan operates, also when ive been driving, turn car off the fans operate for upto a minute before stopping... issues there?

Ive got a brand new sensor spare pm me if your interested?

Green top same part number as above.

i have a similer problem
neither of my fans work.
i have tested them on the battery and both work at high speed but not the slow speed (im guessing the resisters have gone?) my air con pump pumped fine but obviously wasnt getting cold air through unless i was moving above 30mph because the fans dont work. since hearing about this switch box thing under the battery i went and investigated. i found the live down to the slow speed was live at the fans when the terminals were bridged on the control box but there was no live feed at all to the fast speed this is because my 40 amp fuse on the battery has blown when i short the terminals one way on the thermo switch i can hear a clicking coming from the switch box thing under the batery ( proberly the slow speed setting from the thermoswitch) when i try the other way/terminal i get nothing. so im guessing the fault doesnt lie with the thermositch in the rad, but there is a fault
1 - with the rad slow speed resisters = need new fans
2 - the control box under the battery is up the swanny = need new control box

and to make matters worse since i have been fiddling with the control box and such my air con pump no longer pumps. the snowflake symbol is displayed but it definately doesnt work now!!
fink i shud ave stayed in bed

ok from what i know when i had my old polo is that your main fan thats beside your radiater should only kick in when your water temp becomes to high this is sensed by your radiater fan swith that screws into the radiater. i think that the overheating temp is around 100c or sumthing and when this rweachs this it should start up. not too sure about the smaller fan though but this is most likely to do with your air con but as i say im not 100%

To the OP, it sounds like your fan controller and sensors are OK. The only probelm is your larger fan doesn't work.

When you have the AC on, both fans should run at low speed. Try running 12v dirctly to the larger fan. If it works when you ut 12v on the fast input, but not on the slow input, the fan is OK, but the resistor has gone. If it doesn't work at all, it's either a bad ground or the fan is dead.

MK1 Leon TDI; This is a Leon, which is based on the Mk.4 Golf. The radiator fans should come on as I described in post 6 above; both together, on slow at 92 to 97 °C, on fast at 99 to 105 °C, measured by the thermoswitch in the radiator i.e. the temperature of the coolant in the radiator itself.

james butler, the aircon magnetic clutch is also controlled by the fan control unit, so it sounds like you've definitely got a fault there, but it might just be the connector. Your fans are certainly showing the symptoms of burned-out resistors, so it's new fans, wire in external resistors or get a Nime box. You'll still need to get the original fan control box working so the aircon compressor clutch is energised.

cheers muttly, and all you guys for you help. im gonna tear into the car tomorow to try find out what exactlys up with it. ive got an idea (uh oh goes the missis in the background lol) what if i cut out the resisters completely and join the wires have it running fast on both setting inputs. all i can see it doin is cooling a bit faster than its supposed to but it wont cause any problems though will it after all they should only come on when im not moving. probly make the air con work fantastic too!!

cheers muttly, and all you guys for you help. im gonna tear into the car tomorow to try find out what exactlys up with it. ive got an idea (uh oh goes the missis in the background lol) what if i cut out the resisters completely and join the wires have it running fast on both setting inputs. all i can see it doin is cooling a bit faster than its supposed to but it wont cause any problems though will it after all they should only come on when im not moving. probly make the air con work fantastic too!!

The resistors are buried in the fan assemblies, not easy to get at without serious surgery.

I assume you've fixed the 40 Amp fuse? Make sure the contact areas you attached the fuse to are completely clean - if they get corroded the higher resistance makes the assembly get hot and melt the fusebox.

Running the fans at full chat is likely to be very noisy. In the past, people who've run with the low-speed fan fault and not fixed it say that eventually the fans fail - the motors are not supposed to fun at full speed for any length of time, and overheat.

sorry to bring up an old post. Only my small fan runs when AC is on, the larger one doesn't, even when at said 90c and AC on. Checked all fuses on top of battery, and all ok. Do i need to just energize the larger fan to see if it spins, then if it spins, its a control unit under the battery tray thats at fault? Does the large fan only come on for AC? or to help assist the smaller fan cool the engine? Or both?