Peugeot 206 1.4 HDi Stuck in Limp Home Mode

[Mini1976]

I have been trying to fix my car as it won't rev above 2900 rpm and the engine management light (EML) it on. I took the car to a garage & had the codes cleared apart from one that would not clear referring to the "Pre-heating relay circuit spark plugs permanently supplied" which seamed strange as the car starts really well and is a diesel so obviously doesn't have spark plugs. THey then restarted the car and the "Fan assembly low speed control circuit to earth, short circuit to positive, open circuit or actuator malfunction" fault reappeared so I presume this is the issue? I have stripped the cooling fan and found the relay terminals are corroded and one of the wired has come away completely. I have reconnected all items and tested the fan and it seams to work ok now but the EML is still on and it is still in limp home mode. Can anyone help with what might be wrong?

I am a little confused why a faulty fan would cause limp home mode in the first place as the car never over heats and it is a struggle to get the engine hot enough to get the fan to come on in the first place.

Thanks