From the ETM:
The HEVAC panel provides a signal normally at 12
volts for “off” condition and 0 volts for the “on”
condition, which in the case of petrol vehicles is fed
into the ECM and diesel vehicles directly onto the
coil of relay 18. In line is the Air–Conditioning
pressure switch 2, which turns the fans on/off.
When relay 18 is energised, it provides connection
between relays 13 and 14 (fan 1 and 2) in series or
parallel with each other. This is dependent upon the
state of the air–conditioning pressure switch 1.
For the petrol option, when the signal enters the
ECM, the ECM will switch the output on/off to the
fusebox. The ECM will switch the output on
sometimes for engine cooling reasons even though
the engine has been turned off.
Please note that there is a posibility to switch on the left fan for engine cooling. This is what I was referring to.
Your diagnosis that nothing is wrong does not hold water because the fans are switched via relays. The reply given after my first advice was that all relays can be removed but the fan keeps running. a clear sign that there is something wrong.