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BMW M328i, Aux Fan Test

Don’t worry guys, this is the last post today; Just playing catch up. I had my suspicions that the aux fan wasn’t working, and I wanted make sure before it caused issues.

The temp gauge has been pretty stable, but in all the time I have driven the car I haven’t heard the aux fan running, which seemed odd.

The aux fan sits in front of the radiator, and is an electric supplement to the main viscous engine fan. You can just make it out behind the grilles in this photo. Its big.

The aux fan is two-speed, with it turning on low speed at a certain temperature and if the temp still doesn’t come down it will crank up to high speed. At high speed its moving a ton of air, but is very loud.

On the E36 the easiest way to test the fan (other than INPA, which didn’t turn it on) is to jump the connector for the temp sensor on the driver’s side of the radiator.

Disconnect it from the sensor, turn the ignition to ON, and using something metal, bridge two of the terminals. The ground is the bottom pin of the three (looking at the connector head on, with the notch at the top, ground is on the bottom), and the other two pins are the speeds. One should activate low speed when shorted to ground, and the other high speed when shorted to ground.

Low speed

High speed

Now, if your car, like mine, does nothing when you bridge these, the first port of call should be fuses. There will be two fuses for the fan. Check the lid of the fuse box to identify which ones they are, and see if they are blown. One of mine was, it was the smaller of the two, so I popped in a replacement and tested again. This time I had both high and low speeds. Success.

If you still don’t have anything from the fan, turn the ignition off and check the plug for the fan (in the bottom of the fan on my car), and check to see if the fan even physically spins by hand (make sure ignition is OFF first!). You’ll need to do more troubleshooting of our own if you still don’t have any luck, as there are relays that can be tested too.

I haven’t been able to test the temp sensor turns it on automatically yet as I haven’t been able to get the coolant hot enough (my viscous fan is over cooling at the moment; replacement soon), but I’ll keep an ear out for it.

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