Never worked for me and most members here who’ve the problem. Likely his is either a wiring or mechanical issue. For me and most others, it was faulty modules.

 

If one headlight is working normally, then Cee Jay's suggestion to swap the modules seems the obvious logical start. Also, one headlight being 'less bright' sort of screams ground problem to me. And one headlight working fine suggests to me that the ECU is ok. But then what do I know...