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Bypassing this tiny car fan with a resistor to prevent fault reading?

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Jun 20, 2023
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I have this tiny little brushless fan in the car's mirror which has a purpose of blowing fresh air onto humidity and temperature sensors.
Unfortunately they are prone to cause annoying vibrating noise, I have tried a few used ones and all of them did the same. New part is unavailable, producer changed the design to not include the fan anymore but it's not backwards compatible.

I thought about removing the fan completely, by bypassing it with a resistor (otherwise a fault is recorded in the AC module and there are no sensor readings if I just unplug the ground wire from the fan) but my electronics knowledge is so basic and limited that I could not cope with it. Did a few measurements though.

There is 12v and GND going into the fan, but then the 12V kinda "continues" through the fan into the sensor board.
During operation at 12.09V, the voltage on this "output" drops to 11.16V. Resistance measured between the two red wires shows 22Ohm. When I stopped the fan using my fingers, the voltage started dropping more (to 10V etc)
Resistance between GND and 12V input is around 477 Ohm, whereas resistance between GND and the 12v "output" is 450 Ohm.



This is the connection schematic from VISU

Could you help me out bypass this annoying fan completely or at least slow down the RPMs to mute it a little? Or is it even possible to achieve?
I guess I could put a resistor between the 12V input wire, but that would also lower the voltage on the "output" which I'm not sure what it even is.

I would disconnect all wires into the fan (remove the fan), leave the black disconected and install a 22 ohm resistor between red ends.

You might look to the physical / mechanical, like bed or bond
the motor to a more massive object with a soft adhesive, or even
double-stick foam tape. Perhaps damping is enough.

Another option is to relocate the entire assemly to a less
annoying location. Like, when I found that my IAT resistor in the
MAF sensor was getting heat soaked and bothering my hot-start
behavior*, I found the PCM connector pins for it and substituted
a whole 'nother one out in the cowl inlets. Looks like "not the kind
of thing that likes to get wet" but you could figure out a reasonable
location I expect, or fab a little box with protected inlet / outlet.

* not a Honda vehicle, not factory tune....

I would disconnect all wires into the fan (remove the fan), leave the black disconected and install a 22 ohm resistor between red ends.
Well, I thought about it but won't the computer catch an error if the ground is unconnected? Last time I tried just unsoldering the black wire, it threw a "microturbine circuit open" error and the sensor readings were out of scale. This caused the climatronic to not function properly. Might try it though.

I also thought about adding a resistor in front of the fan (to slow it down) and unsoldering the red "output" wire to let it through another 22Ohm resistor so it still has correct voltage (since the voltage drop through the fan would be larger now)

Which is also why I can't move this to any other place, it's situated close to the windshield so it knows when it fogs etc. and the fan is there to take fresh air from the cabin onto the sensors.
I tried putting some rubber, grease and stuff to quieten it but it seems that it's just the fan worn out and produces this noise. It does it even when powered on outside of the car.

Perhaps you can divorce the "sensors need airflow to monitor"
from "BCM be's whiney bitch when motor is not actively sensed".
Like leave the present motor hooked up but put away in a quiet
box, and get a tiny "12V" muffin fan or mini blower (check surplus
PC motherboards) and a bit of tubing...

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