BMW E70 cooling fan not working

[binbin93]

Hi everyone, I’m troubleshooting the electric cooling fan on my 2007 BMW X5 E70 3.0si (N52, built 09/2007).

* Cooling fan does not run.
* I replaced the fan with another known-good fan, but it still does not run.
* I checked the K9137 cooling fan relay.
* F171 100A fuse has been checked and appears good.
* Battery voltage is about 12V with engine off.
* With the K9137 relay removed and the engine running, the B+ input terminal of the relay has only ~2.3V
* The small 2-wire control connector at the relay measures around 4.4V.

My main question is:

Why is the K9137 relay B+ input only ~2.3V when the engine is running, instead of ~12–14V? Where does the B+ supply to K9137 come from, and are there any intermediate connectors, fuses, or power-distribution points between F171 and K9137 on this E70?

Any advice on the correct wiring/power path and recommended tests would be greatly appreciated. Thank you!

[80stech]

It would be good to know some history but you really need to get yourself a wiring diagram.

[josiahg52]

Is F171 fuse good or not? It can be objectively verified with an ohmmeter.

[binbin93]

It is confirmed all fuses related to cooling fan are normal
one more thing I would like to update that DC power In and Out of the relay is 12v after the car sleeping overnight.
as such I see DC voltage power to the cooling fan is not constant at 12v, sometimes drops to 2v

[binbin93]

I have narrowed down the problem. It involves an intermittent voltage drop at the inlet of the relay (7 661 503), but I do not know where this thick red cable originates to check it. I reviewed some wiring diagrams for the X5 E70; one states that the main 12V power to the relay comes from F171 on the battery distribution board, while another shows it coming from F45 in the front fuse box. Could you please advise me on which configuration is correct for my September 2007 BMW X5 3.0si?"

Thank You!