Has anyone got any electrical details regarding the radiator fan? This is a BWA engine on a MKII VRS.. I have established there is a PWM signal on one of the control wires from the ECU, there is another wire that is always high. Problem is that after the fan got jammed, after replacing the 50A midi fuse the fan stays on permanently. My instinct tells me the system works like this - PWM controls slow speed of both fans, the other wire turns the main radiator fan to maximum.

We are just trying to reverse engineer the motor controller atm but this is proving difficult with all the potting compound used! I have established there seems to be nothing wrong with any of the transistors now.

Is that signal wire stuck at 12V from the ECU or directly from an over-temp stat or similar??

I have identified the shorted transistor... Hopefully the fan will be fixable. Not worth the job unless you have the facilities, patience and time, but the transistors are a few pence each at least!
 

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looking forward to a resolution on this being posted.

 

 

Successfully completed the repair. Just one transistor had shorted internally and after scraping the resin off I was able to replace it.

Here are the photos.

https://photos.app.goo.gl/BfdVwtcQPqwTCGC32

Probably not an idea DIY repair but certainly doable. I had to use a grinder on the motor casing but on putting back in to the fan housing it is held together adequately.
Transistor cost a couple of quid. The heat sink was metal so a mica insulating washer had to be used.