these cant be tested by hooking up to a battery - they have a special "command" signal from ECU to turn on - 30/60/90% etc

these can be tested by good OBD2 code scanners

Yep - like INPA on a laptop. I use INPA to check my fan occasionally - usually when I do an oil service and I run a few other checks at the same time (reads errors and info. etc.).

They can also be tested by removing the connector in coolant temp sensor switch in the lower rad hose and inserting a jumper.

Hey wpoll.. can you eloberate on this procedure? Mine broke the second time in 2 years. Searched several sites with no success. Really appreciate if you could.
Thank yo in advance :)

Sure thing - there's a menu in INPA once you are connected to the DME (DDE in my case) called "Activate" - usually F6 - then you can use the F1 and F2 keys to turn the fan on and off again. It's a little slow to respond, so turn it on, give a second or two to start spinning, then leave it for 15-30 seconds to get up to full speed and stabilise, then turn it off. Al the this is with the ignition on but the engine not running. Watch your battery levels and don't leave the car or fan turned on too long, as this electrical state may deplete your battery in 10-15 mins (or less!).

Quick and easy way to test whether the aux fan is dead or not-

Unplug the A/C high pressure switch.
Start the car with the A/C switched on, the Aux fan should run full noise (fail safe) straight away.

If it does not - time for new Aux fan.

Now i have to research on INPA [emoji1] Because i don't have it nor i have seen it.
Thanks anyways wpoll .

I have two fans that don't work. I replaced when it won't work without diagnosing the problem. Now i want test before i decide to buy a new one.

BTW ..NZBM can you please point me to the location of the A/C high pressure switch.

I will search for it too

Thanks

Its on the aluminium A/C Pipe that's clipped to the chassis rail- very close to the lower radiator hose.