Clio preheating lamp and check engine light

Sounds familiar! I had a similar issue with my Clio (though it's an older model). The preheating lamp issue, along with the check engine light, can be a real pain. Smoke when accelerating is definitely not a good sign. Have you tried checking the error codes? That might give you a better idea of what's going on before you start replacing parts.

I haven't checked the error codes yet. Are you suggesting the error codes will directly point to the glow control unit or something else? I'm trying to avoid unnecessary diagnostics costs.

The error codes might not say 'glow control unit defective' explicitly, but they should give you a general area to investigate. I'd recommend getting it checked at a reputable workshop, especially since you already suspect a cable or plug issue related to the control unit. It's better to be safe than sorry when it comes to diesel engines, especially with that mileage.

Thanks for the advice. Indeed, it was the glow control unit. A defective cable/plug connection caused the issue. The repair set me back 95€.