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2003 Passat 1.8t Wagon, GLS AWM engine code.
I bought this vehicle while living in the mountains, now I am in a wrm climate, have found a connection under the hood by the power steering pump area, when I connect the connectors my electric cooling fan comes on and will stay on until the battery is dead, no matter what the temp is. I am having to plug it in when driving so my car will not overheat when sitting in traffic or at a stop, then unplug the connectors when I stop driving. Anyone have an idea of what is going on? Thank you.
:banghead::mad:
 

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I had the same issue with my 98 GLS. I pulled a relay from the cluster under the steering column. ( I don’t remember which one.)
It stopped running constantly and now kicks in when the ac is on.


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Following as mine will randomly start and stop all the time no matter cold or hot.
The random behavior of the fan is normal. It starts when the temp gets to a predefined in the ECM. But if the fan runs constantly I think the relay has closed and stuck. Changing the relay should resolve the issue. At its minimum it should be tested for proper functioning.
 

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If the A/C is not switched on, then the signal to turn on the aux fan should be coming from the thermal fan switch in the bottom radiator hose connection.
Correct, and the clue is that the fan runs when the (faulty) radiator temp switch is plugged in. To the OP: I wouldn't waste time plugging/unplugging that thing, because the only time it would switch on the fan is if the mechanical fan wasn't working, or a high-load and low speed situation was occurring. Watch your temperature indicator, and if it points at the middle of the range, it's not overheating.
 

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I concur with post #5, faulty thermal fan switch, if that's what the OP is unplugging.

Correct operation of the electric fan is as follows:

The fan has two speeds, low and high. Low is powered via a resistor, high directly from battery voltage (via a fuse).

With A/C off and engine at normal temperatures or cold, fan is off. The fan can be called for by either the A/C or the coolant temperature.

When the A/C is switched on, the fan runs in low speed.
If the A/C refrigerant high pressure switch closes, the fan runs in high speed.

The engine coolant temperature switch is located at the radiator bottom connection, just behind the fans. (Not to be confused with the coolant temperature sensor, an analog sensor back near the firewall.) The switch has two separate contacts which close at different temperatures.

When the first speed contact closes, 197 to 206°F, the fan runs at low speed.
When the high speed contact closes, 210 to 221°F, the fan runs at high speed.

(The fan runs at the highest speed demanded by either the A/C or coolant temperature switch.)

The above activate the low and high speed fan relays under the dash, which switch power to the fan motor. In the V6, the relays are integrated in a fan control module under the hood; it also controls the afterrun coolant pump (not present in the 1.8T).
 

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Thank you for the replies. I will go a head and change out the sensor at the radiator and see what happens. Will I need to bleed the cooling system after this? The part that Vagguy linked me too doesn't appear to have any O ring so I am guessing I won't but want to double check....

If the sensor doesn't fix the issue. I will move on to the relay.

Thank you
 

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jjpark, you could simply unplug the coolant thermal switch at the radiator for troubleshooting--just watch your temperature gauge. Except in really hot weather with stop & go traffic, the mechanical fan is plenty adequate (presuming the viscous clutch is in good condition).

Another item worth mentioning: for some time, one of the third-party parts lookup systems had the wrong part identified for the coolant thermal switch. They would sell you a temperature sensor instead... not good.

Both the coolant thermal switch and coolant temperature sensor will fit in either location and will plug in. But they are electrically completely different:

> Coolant thermal switch, lower radiator pipe: contains two switches, normally open, close on high temperature (see Post #8)

> Coolant temperature sensor, rear of engine near firewall: contains two thermistors which vary in resistance with temperature. One thermistor is wired to the ECM, the other to the temperature gauge. They measure 1.5-2.0 kOhm at 30°C, 275-375 Ohms at 80°C (see Bentley G24-5 for graphs).

So, if a previous owner installed a temperature sensor instead of a thermal switch, your fan might operate strangely. You could verify this with an ohmmeter on the Coolant thermal switch. It should measure open circuit unless the engine is hot, nearly zero ohms if it is.
 

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I wonder if Gypsy fixed their issue....and jjpark too.
I have not :icon_eek: Life got in the way and now it's been super hot recently so I haven't really though about it. I do think my main fans clutch is on it's way out as I think it is one of the chirping noises I have had for some time.
 
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