The C30 came in 2 versions, those with front Fog lights used the headlights as DRLs, and those without had DRLs placed where the fog lights normally are. The dash switch for the lights are also different. See page 66 of the owner's manual.

I am afraid that your 'mod' will be more than a simple software 'fix'.

On the other hand, don't fret over it. The fog lights are a poor excuse for good lighting in low visibility settings. They are not bright enough to shine down the road and do not have a very good flat cutoff. On earlier Volvos, I thought they were only used as eye candy and a waste of time and money. Of course, I come from a rallying background where fogs were yellow and had 100000 candle power!
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My name is Klaus and I am a V♂lv♂holic