120i Cooling Fan

[gstsaver]

Hi,

Anyone have a good way to diagnose the cooling fan in E87 120i N46 engine?

The radiator fan only turns on when air con is on and even then only low setting.

When I unplug fan and plug back in when running it cycles through on high speed for a couple minutes.

I checked voltage on the harness coming in and I get 12v on the power wire and the little wire goes to about 3.45v when ignition is on.

I don't know where the relay is for it, but assume that's not the issue since it is getting power, unless it grounds it or the small wire is supposed to go to a slightly higher voltage.
I don't think there is a separate controller...or if so it isn't exposed like the used ones I see for sale for it.
Fan part is 16.32-6 937 515

[gstsaver]

Nobody ever having a cooling fan issue in a 120i? Guess I am the first one.

[MarcoZandrini]

The radiator fan gets power at all times. It’s controlled by the engine computer (DME in BMWspeak) via the small gauge wire. The DME uses pulse width modulation to manage the fan’s speed. Here’s the Wikipedia article on PWM: https://en.m.wikipedia.org/wiki/Pulse-width_modulation

The first step in diagnosing a problem is to scan the DME for codes. The Service Engine Soon light is on only when an emissions related code is present.