Ulysee preheating lamp and smoke

That sounds familiar! I have a Fiat Ulysee as well, though I can't recall the exact year. I experienced similar symptoms – the persistent preheating lamp, the dreaded check engine light, and the puff of smoke when I put my foot down. It definitely points to the preheating system. Have you checked the glow plugs themselves? Sometimes a faulty glow plug can throw the whole system into disarray.

Thank you for your response. I have not yet checked the glow plugs directly. Is this a straightforward process, or does it require specialized tools or knowledge? Could a single faulty glow plug really cause all of the described symptoms?

It's not terribly difficult to check the glow plugs, but you'll need a multimeter and possibly a glow plug socket. You're looking for continuity. A completely dead glow plug could certainly cause the issues you're seeing. However, given the smoke and the fact that the light won't switch off, it might be best to have a workshop take a look. They can properly diagnose the preheating control unit and rule out other possibilities.

I appreciate the advice. I took it to a workshop. As suspected, it was the preheating control unit with a defective plug connection. The repair cost 95€. Thanks again for confirming my suspicions.