Kangoo preheating lamp stays on

Sounds like it could be the glow control unit, yeah. Is the engine misfiring at all, especially when it's cold? If the glow plugs aren't heating properly, that could explain the smoke and the engine light. Maybe try checking the voltage at the glow plugs themselves to see if they're getting power. Could be a faulty sensor somewhere too. I had a similar issue on another diesel car once.

Thanks for the reply. How exactly do I check the voltage at the glow plugs? I'm not super experienced with this kind of thing, so any pointers would be helpful. Also, would a faulty sensor definitely trigger the engine light, or could it be something else entirely?

Checking the voltage requires a multimeter. You'll need to find the positive terminal on each glow plug and test if it's getting voltage when the preheating should be active (when you first turn the key). Be careful not to short anything out! And yeah, a faulty sensor can definitely trigger the engine light, but it's hard to say for sure without a proper diagnostic scan. It's probably best to take it to a workshop to get it checked out.

Cheers, I appreciate the advice. Took it to a local mechanic, and you were right; it was the glow control unit. Turns out a connector was corroded. Repair cost me 95€, which isn't too bad. Thanks again for your help!