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I have a 2008 Volkswagen Jetta S and it cooling fans are supposed to run when the engine gets too hot as expected. But out of 2 fans, the smaller fan is not running.

Could it be because of a blown out fuse? How do I know that the assembly really needs replaced?

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    Are you sure that both fans are supposed to be running? because in most cars one is for the AC and one is for the radiator, try turning on the AC and see if it runs
    – method
    Oct 7, 2016 at 23:41
  • I ran the AC and the small fan ran as you suggested, though it makes some noise. So that shouldn't be the reason my engine light came on as the repair shop said? They also cleared the error logs for some reason.
    – blueseal
    Oct 8, 2016 at 0:23
  • Did the check engine light come back on after they cleared the codes? Also, did they give you the exact codes which they pulled? I'm talking the numbers.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 8, 2016 at 1:52
  • If you live in the U.S you can go to autozone or advanced auto parts and they will scan your vehicle for free. Get the code and look it up to see which sensor it is
    – method
    Oct 8, 2016 at 2:00
  • I live in the US, and I didn't happen to meet a competent Autozone employee the time I went in. He told me he couldn't check it since the light was off then, and he and I didn't know about the error logs. As I stated earlier, the repair shop cleared the logs.
    – blueseal
    Oct 8, 2016 at 18:46

1 Answer 1

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The two fans have different purposes:

  • The big fan provides cooling air for the main radiator. It is the one that runs when the engine needs more cooling.

  • The small fan is for the A/C condenser, it runs when the A/C is active. To make it run (or see that you have a problem) turn on the A/C and put the fan at a non-zero speed. The fan should start running at its slow speed.

On the Mk5 (and later?) cars this means setting a low temperature and making sure that the A/C in not in ECON mode. The fan will only run when temperatures are above freezing and if the A/C system is charged with refrigerant.

So, first thing to do it stop make sure that the small fan should be running by ensuring that the A/C is on. Then if it isn't running:

  1. Test the fan - try turning it by hand to see if it is free, then pull the connector and apply power directly to the fan to see if it runs, you could also meter it to see if the circuit is open. It seems that a common failure on these fans is for a brush to hang up and wear to the point that it no longer makes contact. If that's your problem, this video may help if you want to try your hand at repairing it. Otherwise replace the fan. It's not too hard.

  2. If the fan is good then the problem is either that the A/C needs servicing or that the fan control module has failed. If you A/C isn't blowing cold that's where I'd start.

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