Today at Atelier Kaz - ex-Honda R&D, F1, Indy/CART engineer

The Cooling Fan Control Unit will fail in the same way as
the famous problematic Main Relay.

It is caused by the multiple cracks of the solder on the circuit board,
same issue as the Main Relay.

The symptom depends on where the cracks occurred and
it could randomly switch on and off the radiator and
even the engine bay fans.
If your A/C CCU is also having problem, again,
it could randomly switch on and off the R & L A/C condenser fan
and the compressor itself.


While helping another owner for several issues,
I found that his radiator fan was operating at max speed and
even the engine bay fan was switched on
when the engine was just started.

In fact, both fans operated as soon as I turned the
IG key into ON position.


Typical cooling fan control unit failure.


Under normal circumstances, I have never seen this
engine bay fan in operation.
Honda also removed it from the engine bay on later MT models
so some of the owners won’t even know that there was a cooling
fan inside the engine bay.







I took some video but forgot to hide the mileage counter
and also the VIN plate so the owner is the only one who can
view the full length video but you can see the editted version
showing the engine bay cooling fan in operation.

If you pause the video at the final frame, you can
just about see the engine temperature gauge still at the bottom
even when the engine bay fan was in operation.








The cause of the issue.

May not be easy to see unless you enlarge this photo but
lots and lots of cracks at the IC soldering joints and other areas.

The same cracks can happen at the base of the connector as well.


I always carry spare main relay and this cooling fan control unit on
my NSX just in case another owner may experience the issue
during one of the NSXCB meetings or on the road.


So, as a quick check, used my spare unit and confirmed that the
issue could be fixed by using mine.








Removed the original one, re-soldered all of the joints and
now the radiator fan operates at the low speed when
the engine has warmed up and never saw the engine bay fan
to operate again at idle rpm.


Done.


Kaz