2000 A6 Quattro Avaunt
Auxillary radiator fan turns on and off on as needed when car is running, but stopps immediately when the key switch is turned off. this occasionally depending on day temperature and driving conditions results in audible boiling and bubbles in the coolant resivoir tank and some times in coolant being pushed past the overpressure relaease in the tank cap dripping directly on the exaust. white smoke rolling up out of the engine compartment shortly after you stop is a bit alarming LOL.

I suspect either the control module for the continued circulation coolant pump and radiator fan or the fuse that supplies it with power.

Does the diagnosis sound right?
How to locate these components?

help appreciated
Brian

 

Is this happening as soon as you turn off the car? Like you notice white smoke and bubbles right away as soon as the engine is turned off? If so, this doesn't sound like an aux. fan issue, but more so an overheat condition caused by something else. If this is the case, no matter how hard that little auxiliary fan runs, you will still be encountering the over heat condition, and as temperatures begin to rise outside, it will only happen faster and faster.

I would first have the system pressure tested to see if there are any leaks. They are the usual culprits when you have coolant boiling; More pressure = higher boiling point, lower pressure = lower boiling point for coolant.

The FCM (Fan control module) should be above your oil filter / oil cooler. It's a small metal box with fins on it, and I believe three connectors running to it.

 

Only happens sporadically anD usually the leak and smoke issue takes a minute or two to develop not immediate. thanks for the location of the fan module that helps.
ANy Idea where the fuse for it is located? Or IF it has a seperate fuse for the Vehicle Switch off state?
Regards,
Brian