2005 Jetta Cooling Fan Continuously Running

• #1

In prepping for a 2K trip next week, there couple of quibbles I need to address.

Both cooling fans run constantly. The AC is off. Engine cold, start up, and they both run continuously. Key off, and they both stop. Not sure about the different speeds, but I venture to say it is high speed. I suspect this is not normal. However, the AC does work good! I've only been driving this for the last month, and have never noticed this before. Maybe I have overlooked it, but I am sure to a reasonable degree it is a new occurrence. Any input on troubleshooting and addressing this? Thanks.

• #3

Would you happen to know the Ohm value for the coolant temp sensor? Or any other way to troubleshoot it? Or troubleshoot the fan control module? Thx-

• #5

Thanks all. I will troubleshoot this evening and repair as needed.

• #6

I think you'll find the source of your issue if you patiently go through Dan's excellent diagnostic procedure. I have that same PDF printed and ready to go in my paper drawer myself, and have used it quite often, because it streamlines the process.

Thanks again, Dan!

• #7

Ok, after some troubleshooting with Dan's guide I have some conclusions...and questions.

I can unplug both fans and jump them to the batt. They both run on slow / fast.

I can jump the coolant sensor and get them both to run on slow, but not on fast.

When I unplug the AC (G65?) sensor the fans stop. This was the sensor mounted up near the firewall in the discharge line going to the evaporator.

This leads me to believe it is related to the AC, not necessarily the FCM.
noticed in Dan's guide it said to check the voltage at the white wire on the G65. It should be above VDC, and change proportionately with refrigerant pressure. The wire I have on this are Blue/red, yellow/red, black/white, and black/blue. Not sure which one to test.

I may also add in all the above tests, the engine was off, and AC was in the off position. Any further help would be much appreciated!

• #10

Wow Dan, you are the Fan motor king! I am scrambling to get this resolved before our trip next week. I realize this isn't the worst thing.

Yes, I do have the 4 wire switch. It is mounted up near the fire wall. To be clear, when this is unplugged, the fans both stop.

I will keep you posted as to the pins 3-4 being jumped. I was hesitant to jump any of these no knowing exactly what they are.

As for jumping the "coolant sensor," sorry, wrong nomenclature. I was referring to the radiator thermo switch. 3 wire switch mounted about half way down the radiator. This I can jump and get the fans to run slow, but not fast. Nothing happens on fast.

It seems to me, if the radiator thermo switch was stuck in "very hot," I should still be able to unplug the harness for it, and jump the pins to get both to run on high. I did check all the fuses you mentioned. All are good, and very clean. Any idea where to go from here? Troubleshoot and check the 4 wire AC switch? Thanks again for weighing in with your experience

• #12

Hi again Dan. I see a flaw in my troubleshooting from your last post.

I need to test the radiator thermo switch for fast fan speed with the IGNITION ON. I was checking this with the key in the off position.

I will then proceed to jumping pins 1-2 of the F129 switch. I will keep you posted shortly-

• #13

That 4-pin refrigerant pressure switch was a common failure on the A3 cars, and its failure mode would cause the fan to run constantly. Never seen it manifest itself in the same manner on an early A4 car, though, but that doesn't mean it couldn't happen.

I'm not sure how similar the two systems are, though. I know the early A4 car is sort of full of leftover A3 bits though, so maybe...

• #14

I saw this on a TDI last year when replacing a clutch master and diagnosing low power, which turned into fixing a botched timing belt replacement. The owner said the previous garage (who did the timing belt) said it was 'normal' for the older cars to do it.

I did some diagnosing and found two tires chafed through. Just a thought if everything else checks out.

• #15

Thanks for the tip off Abacus. Do you happen to recall where you found the chaffing in the wiring / harness? Thanks-

• #16

In the harness within a few feet of the sensor. It was hidden pretty good and I only found it by touch. Just seeing the harness isn't good enough, you need to run your hands & fingers down every inch to feel for anything weird.

• #17

Well, I must thank all for there input here on this. It looks like it was a bad 4 pin AC switch. The fans keep running on fast even with the Rad thermo switch unplugged. I unplug the AC switch and jump out pins 1-2, and the rest of the checks test out good. ( rad thermo switch of fast and slow) I have ordered a new AC switch, and also a radiator thermo switch for good measure. It seems from the long post on cooling fans this can be a troublesome failure point with disastrous consequences if not noticed. So, I will swap out as it looks original. Nice to find a good group that is very knowable and willing to weigh in with their input. Thanks again for the help with troubleshooting!

• #19

Hey i have a similar issue but a little different. I have a 2000 jetta tdi, and my cooling fans are always on even when the motor is cold as long as the ac switch is on. If i turn the ac switch to off both of the cooling fans turn off. I noticed this issue right when it got cold here in Spokane Wa and the car started taking way too long to fully warm up ( like 20 min of driving before it warms up) then i noticed the fans always staying on since i always had the ac switched on, and that the fans quit when the ac is switched off. Is this normal for these tdi's ? Any help is much appreciated.

Pretty sure what you describe is normal.

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