So my X5 had the standard aux fan failure. After reading the failures of some cheaper OEM copies and the ridiculous price BMW charge for the OEM part, I looked for an easier (and cheaper solution).

With stand alone ECUs, most use a PWM output to modulate different electrical components and this is exactly what the signal wire for the X5 aux fan is. It is simply a PWM signal wire. The other two wires are power (constant) and an earth.

As with standalone ECUs, a Solid State Relay (SSR) is used to control any normal 12v motor by the PWM signal wire.

So I simply wired up a SSR to the X5 and fitted a normal 16inch thermo fan to the front of the radiator.

It works perfect, just like the OEM and total cost was about $40 for the SSR and $250 for a quality thermo fan.

SSR in Australia https://www.jaycar.com.au/solid-stat...ching/p/SY4086

This is how I wired it up



If you were to do it though, you will probably need a 15inch thermo, the 16 was a little big to fit flat against the radiator (I got creative)