[Darth-Apple]

I drive a 2007 Volkswagen Jetta (2.5 liter). Love the car. It's absolutely amazing and it drives like a dream, save for the electrical problems. We joke that it's possessed by a ghost. Panic alarm goes off on its own. Can't lock with the key fob (triggers alarm also), doors randomly don't latch (already diagnosed this one), windows and sun roof goes up and down on its own on occasion, horn goes off by itself, and all sorts of other mysterious issues. 

Those are all serviceable and able to be worked around, but this particular issue is much worse. The radiator fan is now coming on and off intermittantly, sometimes for seconds, sometimes for hours. It runs the battery down in the middle of the night. I've ordered a new fan relay and will install it tomorrow, but I don't believe this is the issue because I've swapped the ignition/fan relays and had no ignition related issues (they were the same part). Also, as far as I recall, relays fail often but they fail in such a way as to cause them to stick open or close (rather than flicker intermittantly). 

I'm starting to believe this one is a computer module or worse, an actual short in the wiring itself. Shorts (or water) can cause this sort of issue. A lot of people are saying it could be a bad sensor in the radiator as well, although there would be no way to know if it's a bad sensor an actual short itself. 

SpookyZalost is helping me ghetto rig it to only engage the fan when the ignition is on. It's looking like it's going to be a smooth process and won't be too difficult, but I'm wondering if anyone else with German cars has seen this sort of issue before and has any tips for what could be the actual cause itself.

[tc4me]

Hy Darth, So changing the fan from permanent positive (terminal 30) to ignition positive (terminal 15) is not possible with your Jette, because it is regulated by a control unit. In the jet as in the golf, there are 2 typical electrical weak points,
1: The electrical ignition part, spare part: febi bilstein 38638 ignition switch
and the 2 is more true. the control unit:
There are 2 types of construction: the relay / control unit is attached behind the dashboard or by the battery

here are some very good instructions in German
https://www.sgaf.de/content/kuehlerlueft...ayl-437154

tc4me

[SpookyZalost]

@tc4me yes and no.

it is in fact possible if you put a relay in the circuit providing power to the control unit from the fuse box.

just have the relay get it's signal from the ignition's output state (generally the aux line will do).

it won't matter what the control unit is doing because no power will get to the fan until the car is on avoiding battery drain and that's what I recommended darth do, similar to how I linked the additional electrical cooling fan on my jeep to the other so they both use the same control sensor but have separate power circuits.

when one is on, it triggers the relay to pull power from the battery and feed the other, thus the sensor controls both.

just adapting this circuit to read it's on/off signal from the ignition and putting it inline further back in the circuit to the power output from the fuse box means that the sensor won't be able to pull power until the ignition provides power to the relay closing the circuit and providing power along that lead.

Deutsche Übersetzung
[spoiler]
Ja und nein.

Es ist tatsächlich möglich, wenn Sie ein Relais in den Stromkreis einbauen, das die Steuereinheit über den Sicherungskasten mit Strom versorgt.

Lassen Sie das Relais nur das Signal vom Ausgangszustand der Zündung empfangen (im Allgemeinen reicht die Aux-Leitung aus).

Es spielt keine Rolle, was die Steuereinheit tut, da der Lüfter erst dann mit Strom versorgt wird, wenn das Auto eingeschaltet ist. So habe ich darth empfohlen, ähnlich wie ich den zusätzlichen elektrischen Lüfter meines Jeeps mit dem verbunden habe andere, so dass beide den gleichen Steuersensor verwenden, aber separate Stromkreise haben.

Wenn einer eingeschaltet ist, löst er aus, dass das Relais Strom aus der Batterie zieht und den anderen speist, sodass der Sensor beide steuert.

Wenn Sie diesen Stromkreis nur anpassen, um das Ein / Aus-Signal von der Zündung zu lesen, und ihn weiter hinten im Stromkreis an die vom Sicherungskasten ausgegebene Leistung anschließen, kann der Sensor erst dann Strom ziehen, wenn die Zündung die Stromversorgung der Zündung versorgt Relais schließt den Stromkreis und versorgt diese Leitung mit Strom.
[/spoiler]

@Darth-Apple so hey giving it some thought it might be a faulty engine temperature sensor.

is it one radiator fan or two?

if it's one central radiator fan it could be that it's not detecting the temperature properly and being triggered, if multiple and both fans are cutting off/on same thing

if it's just one out of two then it could be a faulty wire in one of them so bypass to control by the other fan using a similar circuit.

apparently the sensor is called an Intake Air Temperature or IAT sensor and is really easy to replace.

costs $16 at any auto parts store.

so try swapping that before you wire in the relay see if it stops it.

if not the relay will at least prevent the issue from occurring when the vehicle is sitting powered off.

[tc4me]

Good morning SpookyZalost

Of course, it is possible to control permanent positive (30) to ignition positive (15) via a normal working relay, I don't know exactly the Jetta, but if there is now a permanent positive on the engine, it is easy, it is controlled via minus from Thermal switch on the cooler. I have a Golf 5 built in 2008 and the fan power supply is controlled directly by a control unit via a relay. There is only electricity plus at the fan motor when the control unit is working everything by Can-bus


My tip, read the errors from the memory, I have the workshop programs such as VCDS or VCP for VW and Audi Porsche. A cheap tool like this one, for example, is sufficient: 

https://www.amazon.com/dp/B07MCJ317T/ref...UTF8&psc=1

Important, simply delete non-open or closed errors, read them out first, write them down, then post them here and only then delete them

[SpookyZalost]

@tc4me glad that's been cleared up.

Honestly I think it's probably the iat sensor as that's what tells the fans to switch on and off and a faulty one would be triggering it so long as they have power.

Having an ignition control to prevent power draw when off is good but it doesn't solve the underlying cause, just prevents it from draining the batteries.
which is probably a good idea regardless since an idle vehicle with power draw is no good unless it's for an accessory plug to use stuff like an air pump or to briefly charge your phone.

It's why my always on accessory on my Jeep has a manual override to bypass the relay and go permanent positive when I need it but is ignition controlled when I don't, to prevent battery drain.

I'm surprised that feature isn't standard lol.

[tc4me]

  Quite my opinion, the vehicles are so littered with electronics and control units, my Audi S6 Performance has 22 control units, you are not even allowed to charge the battery directly, it has to be done via a Can-bus OBD connector. If the batt is defective, the new one must be brought in. it's insane

[SpookyZalost]

@tc4me  what?! that's crazy!

one of my closest friends bought a 2018 subaru and the battery still follows the same rules?! 

why would they make it so you can't directly charge the battery directly?

it's not like those exploding cellphones is it? 

[tc4me]

Here Audi Q Serie its the same