Thanks Alex, that's useful info.

I don't think it would be open collector as the voltage would be pinned to ground and its floating around 2V. I am wondering if the wire is broken and there is some capacitive coupling causing the voltage I'm seeing, so was going to try a 10K resistor to ground to see if it is a real signal or not.

Found the issue, the purple wire was broken.

Carefully stripped back some insulation at the fan controller and ECU to check the continuity to see if the break was at one of the connectors or the main cable run. Was the main cable run so soldered in a new wire and working fine now.

Thanks for the tips. If anyone else has a problem the purple control wire goes to D4 on the first connector on the left at the ECU.

just looked at my 2009,(with stop start)with auto aircon on fans go round,if I turn fan down manually fans stop ,aircon still works but fans stop(engine cold)any thoughts?

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just looked at my 2009,(with stop start)with auto aircon on fans go round,if I turn fan down manually fans stop ,aircon still works but fans stop(engine cold)any thoughts?

I have discovered that I might have the same problem as above. Stuck in traffic on the motorway the temperature gauge went into the red, the high temp warning started to ping and the car steamed up with no air con?

Pulled over switched everything off, opened the bonnet to cool down, only gave it 5 minutes or so as traffic had started to move. Turned ignition back on to check the temperature and back to normal? Once moving the air con was working fine again, I understand why.

Does the temperature gauge also read the air con coolant temperature and then revert back to engine temperature when air con switched off? Its seems odd that the temperature can revert back to normal so quick?

Did some research on here to discover the possible causes and came to the conclusion that it was either the fans defective or the fan control unit.

Tested the fans individually by wiring them directly back to the battery, all ok. Presumed that it must be the control unit. Didn't know how to test it so the only option available was to replace.

Followed one of the links on here which took me to "Partslandrover" on ebay and ordered the part. Richard, the guy who runs the ebay store very kindly gave me a ring to ask me whether I had tested the unit. He has had quite a few returned to him saying they were defective when they were't.

Told him what I had done and he instructed me on the following below procedure to test the fan control unit. I said I would post to help prevent him getting perfectly good units sent back to him.

Fan Control Unit Test

1.Disconnect the main black, red & purple connector on top of the fan control unit.
2.Connect the corresponding terminals on the control unit directly back to the battery. (Red & Black) (Be very careful not to short the wires as its a bit tight in there.)
3.Take a wire from earth (I used the engine block) & pulse a connection onto the small connector that the purple ECU signal wire was connected to. You must pulse the connection not leave it connected or the fans will not start. (Again it is tight in there so be careful not to short anything out.

Once I had completed this test the fans worked, they won't stay on but start up every time the terminal for the purple ECU wire is touched.

I then tested the continuity of the black wire back to earth, all good and the voltage of the red wire which gave me 12v. I then turned the air con on and tested the voltage of the purple ECU signal wire which gave me a reading on 4v.

I'm not sure if this is the correct way to test whether the ECU signal is functioning correctly or not but there is definitely a voltage passing through it.

So I think the only thing left to test is the continuity of the purple ECU signal wire, as above. And see if there is a break in it somewhere, but if there is I wonder why am I getting 4v down it? Could I really be getting a voltage of 4v due to capacitive coupling?

A couple of photos of the fan control unit test cables attached.

Well done useful post.

Thanks for the guidance on this thread.
My aircon isn't working, despite re-gas to 800g/vacuum test and new relays. Honing it down to the cause being either fan module (in accordance to Alex P's description), connection to compressor, or compressor clutch failure. I don't have any electric testing equipment or the knowledge on how to test anything but I have checked the connector into the fan module (appears OK but I haven't seen the fans running for while).
The clutch isn't spinning when I'm asking for aircon. Could anyone give me a brief guide to accessing the compressor wiring connector, is it on top of or below the compressor? I presume with the plastic trim and engine undertray removed it can be reached from below...
Many thanks.