How to Stop a Cooling Fan That Randomly Turns On/Off (Audi A4)

I'm really starting to enjoy my new-to-me 2004 Audi A4 Avant. Like any Euro, it's got a few quirks but overall it's been an honest, fun to drive sports wagon. However, the other day my Audi had its first real "problem."

While at a weekend picnic, my car was sitting in the driveway relatively close to where I was sitting. With music and conversation, it was hard to hear anything other than the ambient sound of the picnic. All of a sudden, a friend turned to me and asked me if I had left my car on. I told him "no, why"? He then told me that it sounded like it was on and after listening very attentively for a second, I could hear what sounded like an idling engine coming from the driveway. As I got closer to my car, I could hear the auxiliary fan spinning at full speed!

Amateur Diagnosis

The car had been sitting for over an hour and the keys were in my pocket. Surely something wasn't right as my car sounded like an airplane on take off. I turned the ignition to the second position and immediately the fan shut off. I pulled the key out and walked away a bit confused, trying to convince myself that perhaps what happened was normal when it was hot. Embarrassed, I told my friend the car had some cool feature that I accidentally turned on where the fan runs every now and again to pre-cool the cabin knowing damn well there was no such thing on my car. I also wanted to hear if it would happen again so I listened very closely for it. Sure enough, about 45 min later the fan came back on and required the ignition to be switched on to turn it off.

After doing some research, it seemed as though this was a problem that had affected a decent number of B6 owners. The root of the problem involves clogged drains and/or a cracked ECU box. A few weeks back, I had to drive the car home in a torrential downpour, so if water was going to get anywhere it shouldn't have, that was the time!

Corroded Relay

Essentially, what can happen is water can get into your ECU box and cause a small pool to form in the bottom which, in some cases, can submerge relay 219 (which operates the fan). If this happens, the internals and contacts of the relay can become corroded and cause the fan to act erratically. If this has happened to you, you will need to replace this relay and either clear your drains so that water will no longer pool OR replace your cracked, broken ECU lid.

What You'll Need

• T30 Torx driver/socket
• Relay P/N: 443-951-253-AA

Accessing the relay is fairly straightforward. Begin by removing the weather strip and then the plastic cover that goes over the battery, ECU box and cabin air filter housing. Your ECU box is located on the right hand side of the engine bay.

Remove the three T30 Torx screws in the front of the box.

My ECU lid was missing the left right screw and it seems as though a lazy mechanic had just broken it off at the back right one due to the need to pull the wipers off to access that screw. Therefore, after removing these three screws I could pull mine out. The proper way to access these final two screws is to remove the right wiper, allowing you to move the plastic shield enough to access this rear screw. Replace the ECU cover if it is compromised in any way.

On some models, like mine, there is a metal clip which bridges across the ECU itself. Push down on either end of it to release the clip.

You can then lift the ECU out of the way which will reveal the 219 fan control relay. Note the evidence of water in the ECU box from the settled orange "rust dust". It seems as though the other two relays have been unaffected by the presence of water in the box...or at least to my knowledge. It may take some patience trying to wiggle the relay out (the corrosion doesn't help).

Once you remove the old one, ensure that the internal contexts aren't compromised. Pop the new relay in and re-install the ECU and cover (properly!). Also, use this experience as a friendly reminder to check all of your drains to ensure they are clean and functioning properly. Now you can relax knowing your fans are no longer haunted! Have you experienced unusual behavior from your car? Let us know in the comments.

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Written by :

Noah Jenkins

Noah Jenkins is attending the University of Connecticut studying Electrical Engineering. He’s been around Volvos since birth. His knowledge and interest in European vehicles expands to Audi, BMW and Land Rover as well. He currently drives and maintains a 2004 Audi A4 Avant and a 1996 Volvo 850