Help diagnosing coolant fan always on

[Tom Vernon]

Hi all, I'm having trouble figuring out why the coolant fan is always on full when the engine is running on my 2007 w203 C180 Kompressor.

It seemed to start around the same time as the AC was getting a bit weak, so I did a scan and sure enough it was throwing a low AC gas pressure code. Assuming it was connected, and as it needed it anyway, I just had the AC gas recharged which sorted the AC and the low gas pressure code but the fan is still always on.

I don't think it's the main coolant temerature sensor as that seems to be functioning fine, but I am aware that it might be using further inputs to determine when to turn the fan on but no idea what they could be.

Is there a relay somewhere that could be malfunctioning? Any other ideas what to check/look for?

 

[AlanGunn]

Does it still run with the A/C off.

 

[Tom Vernon]

Yes, it runs no matter what when the engine is running.

 

[ajlsl600]

Fan trigger swith/sensor failure or wiring to/from ecu issue , default, fan runs continuously? No known basis for this, seems logical.