Modus preheating lamp stays on

Yep, sounds familiar! I had a similar issue with my Modus. The glow plug light staying on and the engine light coming on points to the preheating system. The smoke could be unburnt fuel due to incorrect preheating. Check the cable and plug connection of the preheating control unit first. It's often just a bad connection.

Thanks! Where exactly is that control unit located? And is it easy to check the cable and plug myself?

On the Modus, it's usually near the engine block, often tucked away near the battery or the ECU. Honestly, if you're not comfortable with car electrics, I'd advise against poking around too much. A defective cable or plug connection can cause all sorts of issues. Best to get it checked at a workshop. It could save you a lot of hassle down the line.

Thanks for the advice! Took it to a shop, and you were right, the cable was defective. Cost me 95€ to fix.