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Join Date: May 2011
Posts: 1
2000 328i fan/controller question

Hello All, new member with a question.

Car is a 2000 328i, manual trans w/AC (if that matters).

Recently, the coolant overflow/expansion tank ruptured. As is common, this was a symptom of another problem.

The fan does not come on. Most of the time, this is not a problem. Afternoons in traffic, it's a problem. Unfortunately, it's hard to duplicate the necessary test conditions at home, and I'm hesitant to drive it much in order to duplicate the overheating problem.

My understanding is that the fan controller is not a relay, but a pwm de-modulator, that provides varying fan speeds for different conditions.

The fan itself works (12v applied directly).

My question is how to tell if the problem is a sensor, or the fan controller circuit.

Will an OBDII scanner tell me if there's a bad sensor?

Does anyone know what frequency the pwm signal is? I havn't dragged the 'scope out to the car to check what's on the control signal, but I'm reading either .4 or .04 vdc (forget which). .4vdc, if the meter averages, would indicate about 3% pwm duty cycle - below the 5% cutoff.

Short of building a 50% duty cycle 555 circuit with which to test the controller, does anyone have a suggestion?

I'm fine buying the new fan/shroud/controller assembly, but only if I need it.

Does anyone know what sensor I'd need to test, and how to test it?

Thanks in advance,

Old 05-23-2011, 07:02 AM
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Old 05-23-2011, 07:02 AM

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