manual fan

Are you wanting to override the automatic fan controls to manually lock the fan in?

 

you can use ECM inputs programmed to fan override. One additional wire and some work with DDRS

 

My trainer had a manual switch and the fan still came on automatic. Don't knwo how it is done but yes it can be done.

 

It is easy to do with DDRS, one wire and one switch)

Use any unused input and program it as fan override

 

Easy way is to put switch in to cut power to fan solenoid.
Switch off = no power = fan locked in.
Switch on = fan cuts in and out automatically.

 

and you get fault code every time you use overide switch

 

Not on Detroit DDEC engines. This is the way most trucks are wired up here.
Not sure about Cummins or Cat.

 

Not with DEEC-III ore DEEC-IV. DDEC6 stores all solenoid codes, all Mercedes ECMs (really Temic) do it too.

 

True.
Probably about time slisetski came back to tell us exactly what engine he has. We could them give him the correct information, instead of making wild guesses.
I just gave answer for DDECIII/IV Series60, my favourite engine.