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Old 06-17-2013, 09:13 AM
markuk markuk is offline
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Location: uk
Join Date: Jun 2013
Posts: 1
Mein Auto: 320i
E91 Radiator Fan Not Switching On


I have a 2006 320i (petrol/manual).

For some reason my radiator fan wont run. A couple of weeks ago when I was stuck in traffic for about 10 minutes and the temperature warning light (amber) came on. I immediately turned off the AC (which is generally always on). Within a few seconds the traffic cleared a bit and I was able to drive off. About 30 seconds later the warning light went off and by then I was nearly home. The following morning I checked the coolant level and it was fine.

A few days later I was once again stuck in traffic, this time without the AC on. After about 15 minutes of crawling along, the same warning light came on. I immediately turned the car around (out of the traffic jam) and shortly afterwards the warning light went off.

So, after some initial trial-and-error I've discovered that the radiator fan isn't coming on.

I have a multimeter but I'm a novice at using it, so I've only been able to test some rudimentary things. Here's what I've done.

I disconnected the connector to the fan unit and I can see there is 12v getting to the connector from the engine/battery. The 3rd wire in the connector, which I understand to be the on/off speed control wire, shows 0v without the key in the ignition, it shows about 3.5v with the key in the ignition but without the engine running, and with the engine running (from cold to hot) seems to pulse in the region of 0.21v and 0.24v - it doesn't change. I don't know if I'm measuring this 3rd wire properly!! I connect the common probe on the multimeter to the negative terminal and the DC probe on the multimeter to the 3rd wire. Is that right?

From the connector to the fan motor (ie. through the metal speed control 'box thingy') I can see that there's continuity on both positive and negative wires.

I haven't been able to prise open this box thingy for fear of damaging the rubber/plastic seal.

When the connector is plugged in and the engine has been running for a while, with the AC on, I get 0v at the fan motor (i.e. on the motor side of the box thingy).

The fan spins freely when I spin it by hand. When I feed 12v directly to the fan motor (i.e. by-passing the box thingy), the fan spins up easily and at a noise level that didn't seem unusual.

I've also measured the resistance through the coolant temperature sensor and can confirm that when the temp went up, so did the resistance.

So this is where I am. I'm a bit confused about the readings I got from the 3rd wire at the connector in the various tests I performed. I had expected that the reading on the 3rd wire would change as the engine became hot. Am I testing this correctly? Is there an easy way to send a pulse down that 3rd wire to check that the box thingy is working?

Any help or guidance as to identifying the cause of my problem would be appreciated. Regards Mark
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